diff --git a/CHANGELOG.md b/CHANGELOG.md
index afc34f5..97335e5 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -5,6 +5,33 @@ All notable changes to Terra-View will be documented in this file.
 The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
 and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
+## [0.9.3] - 2026-03-28
+
+### Added
+- **Monitoring Session Detail Page**: New dedicated page for each session showing session info, data files (with View/Report/Download actions), an editable session panel, and report actions.
+- **Session Calendar with Gantt Bars**: Monthly calendar view below the session list, showing each session as a Gantt-style bar. The dim bar represents the full device on/off window; the bright bar highlights the effective recording window. Bars extend edge-to-edge across day cells for sessions spanning midnight.
+- **Configurable Period Windows**: Sessions now store `period_start_hour` and `period_end_hour` to define the exact hours that count toward reports, replacing hardcoded day/night defaults. The session edit panel shows a "Required Recording Window" section with a live preview (e.g. "7:00 AM → 7:00 PM") and a Defaults button that auto-fills based on period type.
+- **Report Date Field**: Sessions can now store an explicit `report_date` to override the automatic target-date heuristic — useful when a device ran across multiple days but only one specific day's data is needed for the report.
+- **Effective Window on Session Info**: Session detail and session cards now show an "Effective" row displaying the computed recording window dates and times in local time.
+- **Vibration Project Redesign**: Vibration project detail page is stripped back to project details and monitoring locations only. Each location supports assigning a seismograph and optional modem. Sound-specific tabs (Schedules, Sessions, Data Files, Assigned Units) are hidden for vibration projects.
+- **Modem Assignment on Locations**: Vibration monitoring locations now support an optional paired modem alongside the seismograph. The swap endpoint handles both assignments atomically, updating bidirectional pairing fields on both units.
+- **Available Modems Endpoint**: New `GET /api/projects/{project_id}/available-modems` endpoint returning all deployed, non-retired modems for use in assignment dropdowns.
+
+### Fixed
+- **Active Assignment Checks**: Unified all `UnitAssignment` "active" checks from `status == "active"` to `assigned_until IS NULL` throughout `project_locations.py` and `projects.py` for consistency with the canonical active definition.
+
+### Changed
+- **Sound-Only Endpoint Guards**: FTP browser, RND viewer, Excel report generation, combined report wizard, and data upload endpoints now return HTTP 400 if called on a non-sound-monitoring project.
+
+### Migration Notes
+Run on each database before deploying:
+```bash
+docker compose exec terra-view python3 backend/migrate_add_session_period_hours.py
+docker compose exec terra-view python3 backend/migrate_add_session_report_date.py
+```
+
+---
+
 ## [0.9.2] - 2026-03-27
 
 ### Added
diff --git a/README.md b/README.md
index 93865ae..d5c7557 100644
--- a/README.md
+++ b/README.md
@@ -1,4 +1,4 @@
-# Terra-View v0.9.2
+# Terra-View v0.9.3
 Backend API and HTMX-powered web interface for managing a mixed fleet of seismographs and field modems. Track deployments, monitor health in real time, merge roster intent with incoming telemetry, and control your fleet through a unified database and dashboard.
 
 ## Features
diff --git a/backend/main.py b/backend/main.py
index 4d9cc1e..89cca81 100644
--- a/backend/main.py
+++ b/backend/main.py
@@ -30,7 +30,7 @@ Base.metadata.create_all(bind=engine)
 ENVIRONMENT = os.getenv("ENVIRONMENT", "production")
 
 # Initialize FastAPI app
-VERSION = "0.9.2"
+VERSION = "0.9.3"
 if ENVIRONMENT == "development":
     _build = os.getenv("BUILD_NUMBER", "0")
     if _build and _build != "0":
@@ -355,8 +355,11 @@ async def nrl_detail_page(
     ).first()
 
     assigned_unit = None
+    assigned_modem = None
     if assignment:
         assigned_unit = db.query(RosterUnit).filter_by(id=assignment.unit_id).first()
+        if assigned_unit and assigned_unit.deployed_with_modem_id:
+            assigned_modem = db.query(RosterUnit).filter_by(id=assigned_unit.deployed_with_modem_id).first()
 
     # Get session count
     session_count = db.query(MonitoringSession).filter_by(location_id=location_id).count()
@@ -393,6 +396,7 @@ async def nrl_detail_page(
         "location": location,
         "assignment": assignment,
         "assigned_unit": assigned_unit,
+        "assigned_modem": assigned_modem,
         "session_count": session_count,
         "file_count": file_count,
         "active_session": active_session,
diff --git a/backend/migrate_add_session_period_hours.py b/backend/migrate_add_session_period_hours.py
new file mode 100644
index 0000000..5cfb0dc
--- /dev/null
+++ b/backend/migrate_add_session_period_hours.py
@@ -0,0 +1,42 @@
+"""
+Migration: add period_start_hour and period_end_hour to monitoring_sessions.
+
+Run once:
+    python backend/migrate_add_session_period_hours.py
+
+Or inside the container:
+    docker exec terra-view python3 backend/migrate_add_session_period_hours.py
+"""
+
+import sys
+import os
+sys.path.insert(0, os.path.dirname(os.path.dirname(os.path.abspath(__file__))))
+
+from backend.database import engine
+from sqlalchemy import text
+
+def run():
+    with engine.connect() as conn:
+        # Check which columns already exist
+        result = conn.execute(text("PRAGMA table_info(monitoring_sessions)"))
+        existing = {row[1] for row in result}
+
+        added = []
+        for col, definition in [
+            ("period_start_hour", "INTEGER"),
+            ("period_end_hour",   "INTEGER"),
+        ]:
+            if col not in existing:
+                conn.execute(text(f"ALTER TABLE monitoring_sessions ADD COLUMN {col} {definition}"))
+                added.append(col)
+            else:
+                print(f"  Column '{col}' already exists — skipping.")
+
+        conn.commit()
+
+        if added:
+            print(f"  Added columns: {', '.join(added)}")
+        print("Migration complete.")
+
+if __name__ == "__main__":
+    run()
diff --git a/backend/migrate_add_session_report_date.py b/backend/migrate_add_session_report_date.py
new file mode 100644
index 0000000..3b17ac7
--- /dev/null
+++ b/backend/migrate_add_session_report_date.py
@@ -0,0 +1,41 @@
+"""
+Migration: add report_date to monitoring_sessions.
+
+Run once:
+    python backend/migrate_add_session_report_date.py
+
+Or inside the container:
+    docker exec terra-view-terra-view-1 python3 backend/migrate_add_session_report_date.py
+"""
+
+import sys
+import os
+sys.path.insert(0, os.path.dirname(os.path.dirname(os.path.abspath(__file__))))
+
+from backend.database import engine
+from sqlalchemy import text
+
+def run():
+    with engine.connect() as conn:
+        # Check which columns already exist
+        result = conn.execute(text("PRAGMA table_info(monitoring_sessions)"))
+        existing = {row[1] for row in result}
+
+        added = []
+        for col, definition in [
+            ("report_date", "DATE"),
+        ]:
+            if col not in existing:
+                conn.execute(text(f"ALTER TABLE monitoring_sessions ADD COLUMN {col} {definition}"))
+                added.append(col)
+            else:
+                print(f"  Column '{col}' already exists — skipping.")
+
+        conn.commit()
+
+        if added:
+            print(f"  Added columns: {', '.join(added)}")
+        print("Migration complete.")
+
+if __name__ == "__main__":
+    run()
diff --git a/backend/models.py b/backend/models.py
index bb0ca10..b45f12f 100644
--- a/backend/models.py
+++ b/backend/models.py
@@ -303,6 +303,17 @@ class MonitoringSession(Base):
     # weekday_day | weekday_night | weekend_day | weekend_night
     period_type = Column(String, nullable=True)
 
+    # Effective monitoring window (hours 0–23).  Night sessions cross midnight
+    # (period_end_hour < period_start_hour).  NULL = no filtering applied.
+    # e.g.  Day: start=7, end=19   Night: start=19, end=7
+    period_start_hour = Column(Integer, nullable=True)
+    period_end_hour   = Column(Integer, nullable=True)
+
+    # For day sessions: the specific calendar date to use for report filtering.
+    # Overrides the automatic "last date with daytime rows" heuristic.
+    # Null = use heuristic.
+    report_date = Column(Date, nullable=True)
+
     # Snapshot of device configuration at recording time
     session_metadata = Column(Text, nullable=True)  # JSON
 
diff --git a/backend/routers/project_locations.py b/backend/routers/project_locations.py
index 44fcdd5..efa21a8 100644
--- a/backend/routers/project_locations.py
+++ b/backend/routers/project_locations.py
@@ -31,10 +31,24 @@ from backend.models import (
     DataFile,
 )
 from backend.templates_config import templates
+from backend.utils.timezone import local_to_utc
 
 router = APIRouter(prefix="/api/projects/{project_id}", tags=["project-locations"])
 
 
+# ============================================================================
+# Shared helpers
+# ============================================================================
+
+def _require_sound_project(project) -> None:
+    """Raise 400 if the project is not a sound_monitoring project."""
+    if not project or project.project_type_id != "sound_monitoring":
+        raise HTTPException(
+            status_code=400,
+            detail="This feature is only available for Sound Monitoring projects.",
+        )
+
+
 # ============================================================================
 # Session period helpers
 # ============================================================================
@@ -98,11 +112,11 @@ async def get_project_locations(
     # Enrich with assignment info
     locations_data = []
     for location in locations:
-        # Get active assignment
+        # Get active assignment (active = assigned_until IS NULL)
         assignment = db.query(UnitAssignment).filter(
             and_(
                 UnitAssignment.location_id == location.id,
-                UnitAssignment.status == "active",
+                UnitAssignment.assigned_until == None,
             )
         ).first()
 
@@ -258,11 +272,11 @@ async def delete_location(
     if not location:
         raise HTTPException(status_code=404, detail="Location not found")
 
-    # Check if location has active assignments
+    # Check if location has active assignments (active = assigned_until IS NULL)
     active_assignments = db.query(UnitAssignment).filter(
         and_(
             UnitAssignment.location_id == location_id,
-            UnitAssignment.status == "active",
+            UnitAssignment.assigned_until == None,
         )
     ).count()
 
@@ -353,18 +367,18 @@ async def assign_unit_to_location(
             detail=f"Unit type '{unit.device_type}' does not match location type '{location.location_type}'",
         )
 
-    # Check if location already has an active assignment
+    # Check if location already has an active assignment (active = assigned_until IS NULL)
     existing_assignment = db.query(UnitAssignment).filter(
         and_(
             UnitAssignment.location_id == location_id,
-            UnitAssignment.status == "active",
+            UnitAssignment.assigned_until == None,
         )
     ).first()
 
     if existing_assignment:
         raise HTTPException(
             status_code=400,
-            detail=f"Location already has an active unit assignment ({existing_assignment.unit_id}). Unassign first.",
+            detail=f"Location already has an active unit assignment ({existing_assignment.unit_id}). Use swap to replace it.",
         )
 
     # Create new assignment
@@ -433,10 +447,120 @@ async def unassign_unit(
     return {"success": True, "message": "Unit unassigned successfully"}
 
 
+@router.post("/locations/{location_id}/swap")
+async def swap_unit_on_location(
+    project_id: str,
+    location_id: str,
+    request: Request,
+    db: Session = Depends(get_db),
+):
+    """
+    Swap the unit assigned to a vibration monitoring location.
+    Ends the current active assignment (if any), creates a new one,
+    and optionally updates modem pairing on the seismograph.
+    Works for first-time assignments too (no current assignment = just create).
+    """
+    location = db.query(MonitoringLocation).filter_by(
+        id=location_id,
+        project_id=project_id,
+    ).first()
+    if not location:
+        raise HTTPException(status_code=404, detail="Location not found")
+
+    form_data = await request.form()
+    unit_id = form_data.get("unit_id")
+    modem_id = form_data.get("modem_id") or None
+    notes = form_data.get("notes") or None
+
+    if not unit_id:
+        raise HTTPException(status_code=400, detail="unit_id is required")
+
+    # Validate new unit
+    unit = db.query(RosterUnit).filter_by(id=unit_id).first()
+    if not unit:
+        raise HTTPException(status_code=404, detail="Unit not found")
+
+    expected_device_type = "slm" if location.location_type == "sound" else "seismograph"
+    if unit.device_type != expected_device_type:
+        raise HTTPException(
+            status_code=400,
+            detail=f"Unit type '{unit.device_type}' does not match location type '{location.location_type}'",
+        )
+
+    # End current active assignment if one exists (active = assigned_until IS NULL)
+    current = db.query(UnitAssignment).filter(
+        and_(
+            UnitAssignment.location_id == location_id,
+            UnitAssignment.assigned_until == None,
+        )
+    ).first()
+    if current:
+        current.assigned_until = datetime.utcnow()
+        current.status = "completed"
+
+    # Create new assignment
+    new_assignment = UnitAssignment(
+        id=str(uuid.uuid4()),
+        unit_id=unit_id,
+        location_id=location_id,
+        project_id=project_id,
+        device_type=unit.device_type,
+        assigned_until=None,
+        status="active",
+        notes=notes,
+    )
+    db.add(new_assignment)
+
+    # Update modem pairing on the seismograph if modem provided
+    if modem_id:
+        modem = db.query(RosterUnit).filter_by(id=modem_id, device_type="modem").first()
+        if not modem:
+            raise HTTPException(status_code=404, detail=f"Modem '{modem_id}' not found")
+        unit.deployed_with_modem_id = modem_id
+        modem.deployed_with_unit_id = unit_id
+    else:
+        # Clear modem pairing if not provided
+        unit.deployed_with_modem_id = None
+
+    db.commit()
+
+    return JSONResponse({
+        "success": True,
+        "assignment_id": new_assignment.id,
+        "message": f"Unit '{unit_id}' assigned to '{location.name}'" + (f" with modem '{modem_id}'" if modem_id else ""),
+    })
+
+
 # ============================================================================
 # Available Units for Assignment
 # ============================================================================
 
+@router.get("/available-modems", response_class=JSONResponse)
+async def get_available_modems(
+    project_id: str,
+    db: Session = Depends(get_db),
+):
+    """
+    Get all deployed, non-retired modems for the modem assignment dropdown.
+    """
+    modems = db.query(RosterUnit).filter(
+        and_(
+            RosterUnit.device_type == "modem",
+            RosterUnit.deployed == True,
+            RosterUnit.retired == False,
+        )
+    ).order_by(RosterUnit.id).all()
+
+    return [
+        {
+            "id": m.id,
+            "hardware_model": m.hardware_model,
+            "ip_address": m.ip_address,
+        }
+        for m in modems
+    ]
+
+
 @router.get("/available-units", response_class=JSONResponse)
 async def get_available_units(
     project_id: str,
@@ -459,9 +583,9 @@ async def get_available_units(
         )
     ).all()
 
-    # Filter out units that already have active assignments
+    # Filter out units that already have active assignments (active = assigned_until IS NULL)
     assigned_unit_ids = db.query(UnitAssignment.unit_id).filter(
-        UnitAssignment.status == "active"
+        UnitAssignment.assigned_until == None
     ).distinct().all()
     assigned_unit_ids = [uid[0] for uid in assigned_unit_ids]
 
@@ -637,6 +761,9 @@ async def upload_nrl_data(
     from datetime import datetime
 
     # Verify project and location exist
+    project = db.query(Project).filter_by(id=project_id).first()
+    _require_sound_project(project)
+
     location = db.query(MonitoringLocation).filter_by(
         id=location_id, project_id=project_id
     ).first()
@@ -698,8 +825,15 @@ async def upload_nrl_data(
             rnh_meta = _parse_rnh(fbytes)
             break
 
-    started_at = _parse_rnh_datetime(rnh_meta.get("start_time_str")) or datetime.utcnow()
-    stopped_at = _parse_rnh_datetime(rnh_meta.get("stop_time_str"))
+    # RNH files store local time (no UTC offset).  Use local values for period
+    # classification / label generation, then convert to UTC for DB storage so
+    # the local_datetime Jinja filter displays the correct time.
+    started_at_local = _parse_rnh_datetime(rnh_meta.get("start_time_str")) or datetime.utcnow()
+    stopped_at_local = _parse_rnh_datetime(rnh_meta.get("stop_time_str"))
+
+    started_at = local_to_utc(started_at_local)
+    stopped_at = local_to_utc(stopped_at_local) if stopped_at_local else None
+
     duration_seconds = None
     if started_at and stopped_at:
         duration_seconds = int((stopped_at - started_at).total_seconds())
@@ -709,8 +843,9 @@ async def upload_nrl_data(
     index_number = rnh_meta.get("index_number", "")
 
     # --- Step 3: Create MonitoringSession ---
-    period_type = _derive_period_type(started_at) if started_at else None
-    session_label = _build_session_label(started_at, location.name, period_type) if started_at else None
+    # Use local times for period/label so classification reflects the clock at the site.
+    period_type = _derive_period_type(started_at_local) if started_at_local else None
+    session_label = _build_session_label(started_at_local, location.name, period_type) if started_at_local else None
 
     session_id = str(uuid.uuid4())
     monitoring_session = MonitoringSession(
@@ -815,15 +950,18 @@ async def get_nrl_live_status(
     Fetch cached status from SLMM for the unit assigned to this NRL and
     return a compact HTML status card. Used in the NRL overview tab for
     connected NRLs. Gracefully shows an offline message if SLMM is unreachable.
+    Sound Monitoring projects only.
     """
     import os
     import httpx
 
-    # Find the assigned unit
+    _require_sound_project(db.query(Project).filter_by(id=project_id).first())
+
+    # Find the assigned unit (active = assigned_until IS NULL)
     assignment = db.query(UnitAssignment).filter(
         and_(
             UnitAssignment.location_id == location_id,
-            UnitAssignment.status == "active",
+            UnitAssignment.assigned_until == None,
         )
     ).first()
 
diff --git a/backend/routers/projects.py b/backend/routers/projects.py
index ee58eb5..43c4d95 100644
--- a/backend/routers/projects.py
+++ b/backend/routers/projects.py
@@ -20,7 +20,7 @@ import json
 import logging
 import io
 
-from backend.utils.timezone import utc_to_local, format_local_datetime
+from backend.utils.timezone import utc_to_local, format_local_datetime, local_to_utc
 
 from backend.database import get_db
 from fastapi import UploadFile, File
@@ -45,6 +45,21 @@ router = APIRouter(prefix="/api/projects", tags=["projects"])
 logger = logging.getLogger(__name__)
 
 
+# ============================================================================
+# Shared helpers
+# ============================================================================
+
+def _require_sound_project(project: Project) -> None:
+    """Raise 400 if the project is not a sound_monitoring project.
+    Call this at the top of any endpoint that only makes sense for sound projects
+    (report generation, FTP browser, RND file viewer, etc.)."""
+    if not project or project.project_type_id != "sound_monitoring":
+        raise HTTPException(
+            status_code=400,
+            detail="This feature is only available for Sound Monitoring projects.",
+        )
+
+
 # ============================================================================
 # RND file normalization — maps AU2 (older Rion) column names to the NL-43
 # equivalents so report generation and the web viewer work for both formats.
@@ -398,11 +413,11 @@ async def get_projects_list(
             project_id=project.id
         ).scalar()
 
-        # Count assigned units
+        # Count assigned units (active = assigned_until IS NULL)
         unit_count = db.query(func.count(UnitAssignment.id)).filter(
             and_(
                 UnitAssignment.project_id == project.id,
-                UnitAssignment.status == "active",
+                UnitAssignment.assigned_until == None,
             )
         ).scalar()
 
@@ -806,11 +821,11 @@ async def get_project_dashboard(
     # Get locations
     locations = db.query(MonitoringLocation).filter_by(project_id=project_id).all()
 
-    # Get assigned units with details
+    # Get assigned units with details (active = assigned_until IS NULL)
     assignments = db.query(UnitAssignment).filter(
         and_(
             UnitAssignment.project_id == project_id,
-            UnitAssignment.status == "active",
+            UnitAssignment.assigned_until == None,
         )
     ).all()
 
@@ -899,11 +914,11 @@ async def get_project_units(
     """
     from backend.models import DataFile
 
-    # Get all assignments for this project
+    # Get all assignments for this project (active = assigned_until IS NULL)
     assignments = db.query(UnitAssignment).filter(
         and_(
             UnitAssignment.project_id == project_id,
-            UnitAssignment.status == "active",
+            UnitAssignment.assigned_until == None,
         )
     ).all()
 
@@ -1128,7 +1143,7 @@ async def get_project_sessions(
 
     sessions = query.order_by(MonitoringSession.started_at.desc()).all()
 
-    # Enrich with unit and location details
+    # Enrich with unit, location, and effective time window details
     sessions_data = []
     for session in sessions:
         unit = None
@@ -1139,10 +1154,34 @@ async def get_project_sessions(
         if session.location_id:
             location = db.query(MonitoringLocation).filter_by(id=session.location_id).first()
 
+        # Compute "Effective: date time → date time" string when period hours are set
+        effective_range = None
+        if session.period_start_hour is not None and session.period_end_hour is not None and session.started_at:
+            from datetime import date as _date
+            local_start = utc_to_local(session.started_at)
+            start_day = session.report_date if session.report_date else local_start.date()
+            sh = session.period_start_hour
+            eh = session.period_end_hour
+
+            def _fmt_h(h):
+                ampm = "AM" if h < 12 else "PM"
+                h12  = h % 12 or 12
+                return f"{h12}:00 {ampm}"
+
+            start_str = f"{start_day.month}/{start_day.day} {_fmt_h(sh)}"
+            if eh > sh:  # same calendar day
+                end_day = start_day
+            else:        # crosses midnight
+                from datetime import timedelta as _td
+                end_day = start_day + _td(days=1)
+            end_str = f"{end_day.month}/{end_day.day} {_fmt_h(eh)}"
+            effective_range = f"{start_str} → {end_str}"
+
         sessions_data.append({
             "session": session,
             "unit": unit,
             "location": location,
+            "effective_range": effective_range,
         })
 
     return templates.TemplateResponse("partials/projects/session_list.html", {
@@ -1152,6 +1191,173 @@ async def get_project_sessions(
     })
 
 
+@router.get("/{project_id}/sessions-calendar", response_class=HTMLResponse)
+async def get_sessions_calendar(
+    project_id: str,
+    request: Request,
+    db: Session = Depends(get_db),
+    month: Optional[int] = Query(None),
+    year: Optional[int] = Query(None),
+):
+    """
+    Monthly calendar view of monitoring sessions.
+    Color-coded by NRL location.  Returns HTML partial.
+    """
+    from calendar import monthrange
+    from datetime import date as _date, timedelta as _td
+
+    # Default to current month
+    now_local = utc_to_local(datetime.utcnow())
+    if not year:
+        year = now_local.year
+    if not month:
+        month = now_local.month
+
+    # Clamp month to valid range
+    month = max(1, min(12, month))
+
+    # Load all sessions for this project
+    sessions = db.query(MonitoringSession).filter_by(project_id=project_id).all()
+
+    # Build location -> color map (deterministic)
+    PALETTE = [
+        "#f97316", "#3b82f6", "#10b981", "#8b5cf6",
+        "#ec4899", "#14b8a6", "#f59e0b", "#6366f1",
+        "#ef4444", "#84cc16",
+    ]
+    loc_ids = sorted({s.location_id for s in sessions if s.location_id})
+    loc_color = {lid: PALETTE[i % len(PALETTE)] for i, lid in enumerate(loc_ids)}
+
+    # Load location names
+    loc_names = {}
+    for lid in loc_ids:
+        loc = db.query(MonitoringLocation).filter_by(id=lid).first()
+        if loc:
+            loc_names[lid] = loc.name
+
+    # Build calendar grid bounds first (needed for session spanning logic)
+    first_day = _date(year, month, 1)
+    last_day = _date(year, month, monthrange(year, month)[1])
+    days_before = (first_day.isoweekday() % 7)
+    grid_start = first_day - _td(days=days_before)
+    days_after = 6 - (last_day.isoweekday() % 7)
+    grid_end = last_day + _td(days=days_after)
+
+    def _period_hours(s):
+        """Return (start_hour, end_hour) for a session, falling back to period_type defaults."""
+        psh, peh = s.period_start_hour, s.period_end_hour
+        if psh is None or peh is None:
+            if s.period_type and "night" in s.period_type:
+                return 19, 7
+            if s.period_type and "day" in s.period_type:
+                return 7, 19
+        return psh, peh
+
+    # Build day -> list of gantt segments
+    day_sessions: dict = {}
+    for s in sessions:
+        if not s.started_at:
+            continue
+        local_start = utc_to_local(s.started_at)
+        local_end = utc_to_local(s.stopped_at) if s.stopped_at else now_local
+        span_start = local_start.date()
+        span_end = local_end.date()
+        psh, peh = _period_hours(s)
+
+        cur_d = span_start
+        while cur_d <= span_end:
+            if grid_start <= cur_d <= grid_end:
+                # Device bar bounds (hours 0–24 within this day)
+                dev_sh = (local_start.hour + local_start.minute / 60.0) if cur_d == span_start else 0.0
+                dev_eh = (local_end.hour + local_end.minute / 60.0) if cur_d == span_end else 24.0
+
+                # Effective window within this day
+                eff_sh = eff_eh = None
+                if psh is not None and peh is not None:
+                    if psh < peh:
+                        # Day window e.g. 7→19
+                        eff_sh, eff_eh = float(psh), float(peh)
+                    else:
+                        # Night window crossing midnight e.g. 19→7
+                        if cur_d == span_start:
+                            eff_sh, eff_eh = float(psh), 24.0
+                        else:
+                            eff_sh, eff_eh = 0.0, float(peh)
+
+                # Format tooltip labels
+                def _fmt_h(h):
+                    hh = int(h) % 24
+                    mm = int((h % 1) * 60)
+                    suffix = "AM" if hh < 12 else "PM"
+                    return f"{hh % 12 or 12}:{mm:02d} {suffix}"
+
+                if cur_d not in day_sessions:
+                    day_sessions[cur_d] = []
+                day_sessions[cur_d].append({
+                    "session_id": s.id,
+                    "label": s.session_label or f"Session {s.id[:8]}",
+                    "location_id": s.location_id,
+                    "location_name": loc_names.get(s.location_id, "Unknown"),
+                    "color": loc_color.get(s.location_id, "#9ca3af"),
+                    "status": s.status,
+                    "period_type": s.period_type,
+                    # Gantt bar percentages (0–100 scale across 24 hours)
+                    "dev_start_pct": round(dev_sh / 24 * 100, 1),
+                    "dev_width_pct": max(1.5, round((dev_eh - dev_sh) / 24 * 100, 1)),
+                    "eff_start_pct": round(eff_sh / 24 * 100, 1) if eff_sh is not None else None,
+                    "eff_width_pct": max(1.0, round((eff_eh - eff_sh) / 24 * 100, 1)) if eff_sh is not None else None,
+                    "dev_start_label": _fmt_h(dev_sh),
+                    "dev_end_label": _fmt_h(dev_eh),
+                    "eff_start_label": f"{int(psh):02d}:00" if eff_sh is not None else None,
+                    "eff_end_label": f"{int(peh):02d}:00" if eff_sh is not None else None,
+                })
+            cur_d += _td(days=1)
+
+    weeks = []
+    cur = grid_start
+    while cur <= grid_end:
+        week = []
+        for _ in range(7):
+            week.append({
+                "date": cur,
+                "in_month": cur.month == month,
+                "is_today": cur == now_local.date(),
+                "sessions": day_sessions.get(cur, []),
+            })
+            cur += _td(days=1)
+        weeks.append(week)
+
+    # Prev/next month navigation
+    prev_month = month - 1 if month > 1 else 12
+    prev_year  = year if month > 1 else year - 1
+    next_month = month + 1 if month < 12 else 1
+    next_year  = year if month < 12 else year + 1
+
+    import calendar as _cal
+    month_name = _cal.month_name[month]
+
+    # Legend: only locations that have sessions this month
+    used_lids = {s["location_id"] for day in day_sessions.values() for s in day}
+    legend = [
+        {"location_id": lid, "name": loc_names.get(lid, lid[:8]), "color": loc_color[lid]}
+        for lid in loc_ids if lid in used_lids
+    ]
+
+    return templates.TemplateResponse("partials/projects/sessions_calendar.html", {
+        "request": request,
+        "project_id": project_id,
+        "weeks": weeks,
+        "month": month,
+        "year": year,
+        "month_name": month_name,
+        "prev_month": prev_month,
+        "prev_year": prev_year,
+        "next_month": next_month,
+        "next_year": next_year,
+        "legend": legend,
+    })
+
+
 @router.get("/{project_id}/ftp-browser", response_class=HTMLResponse)
 async def get_ftp_browser(
     project_id: str,
@@ -1160,15 +1366,18 @@ async def get_ftp_browser(
 ):
     """
     Get FTP browser interface for downloading files from assigned SLMs.
-    Returns HTML partial with FTP browser.
+    Returns HTML partial with FTP browser. Sound Monitoring projects only.
     """
     from backend.models import DataFile
 
-    # Get all assignments for this project
+    project = db.query(Project).filter_by(id=project_id).first()
+    _require_sound_project(project)
+
+    # Get all assignments for this project (active = assigned_until IS NULL)
     assignments = db.query(UnitAssignment).filter(
         and_(
             UnitAssignment.project_id == project_id,
-            UnitAssignment.status == "active",
+            UnitAssignment.assigned_until == None,
         )
     ).all()
 
@@ -1202,6 +1411,7 @@ async def ftp_download_to_server(
     """
     Download a file from an SLM to the server via FTP.
     Creates a DataFile record and stores the file in data/Projects/{project_id}/
+    Sound Monitoring projects only.
     """
     import httpx
     import os
@@ -1209,6 +1419,8 @@ async def ftp_download_to_server(
     from pathlib import Path
     from backend.models import DataFile
 
+    _require_sound_project(db.query(Project).filter_by(id=project_id).first())
+
     data = await request.json()
     unit_id = data.get("unit_id")
     remote_path = data.get("remote_path")
@@ -1367,12 +1579,15 @@ async def ftp_download_folder_to_server(
     Download an entire folder from an SLM to the server via FTP.
     Extracts all files from the ZIP and preserves folder structure.
     Creates individual DataFile records for each file.
+    Sound Monitoring projects only.
     """
     import httpx
     import os
     import hashlib
     import zipfile
     import io
+
+    _require_sound_project(db.query(Project).filter_by(id=project_id).first())
     from pathlib import Path
     from backend.models import DataFile
 
@@ -1800,6 +2015,23 @@ async def delete_session(
 
 VALID_PERIOD_TYPES = {"weekday_day", "weekday_night", "weekend_day", "weekend_night"}
 
+
+def _derive_period_type(dt: datetime) -> str:
+    is_weekend = dt.weekday() >= 5
+    is_night = dt.hour >= 22 or dt.hour < 7
+    if is_weekend:
+        return "weekend_night" if is_night else "weekend_day"
+    return "weekday_night" if is_night else "weekday_day"
+
+
+def _build_session_label(dt: datetime, location_name: str, period_type: str) -> str:
+    day_abbr = dt.strftime("%a")
+    date_str = f"{dt.month}/{dt.day}"
+    period_str = {"weekday_day": "Day", "weekday_night": "Night", "weekend_day": "Day", "weekend_night": "Night"}.get(period_type, "")
+    parts = [p for p in [location_name, f"{day_abbr} {date_str}", period_str] if p]
+    return " — ".join(parts)
+
+
 @router.patch("/{project_id}/sessions/{session_id}")
 async def patch_session(
     project_id: str,
@@ -1807,13 +2039,53 @@ async def patch_session(
     data: dict,
     db: Session = Depends(get_db),
 ):
-    """Update session_label and/or period_type on a monitoring session."""
+    """Update session fields: started_at, stopped_at, session_label, period_type."""
     session = db.query(MonitoringSession).filter_by(id=session_id).first()
     if not session:
         raise HTTPException(status_code=404, detail="Session not found")
     if session.project_id != project_id:
         raise HTTPException(status_code=403, detail="Session does not belong to this project")
 
+    times_changed = False
+
+    if "started_at" in data and data["started_at"]:
+        try:
+            local_dt = datetime.fromisoformat(data["started_at"])
+            session.started_at = local_to_utc(local_dt)
+            times_changed = True
+        except ValueError:
+            raise HTTPException(status_code=400, detail="Invalid started_at datetime format")
+
+    if "stopped_at" in data:
+        if data["stopped_at"]:
+            try:
+                local_dt = datetime.fromisoformat(data["stopped_at"])
+                session.stopped_at = local_to_utc(local_dt)
+                times_changed = True
+            except ValueError:
+                raise HTTPException(status_code=400, detail="Invalid stopped_at datetime format")
+        else:
+            session.stopped_at = None
+            times_changed = True
+
+    if times_changed and session.started_at and session.stopped_at:
+        delta = session.stopped_at - session.started_at
+        session.duration_seconds = max(0, int(delta.total_seconds()))
+    elif times_changed and not session.stopped_at:
+        session.duration_seconds = None
+
+    # Re-derive period_type and session_label from new started_at unless explicitly provided
+    if times_changed and session.started_at and "period_type" not in data:
+        local_start = utc_to_local(session.started_at)
+        session.period_type = _derive_period_type(local_start)
+
+    if times_changed and session.started_at and "session_label" not in data:
+        from backend.models import MonitoringLocation
+        location = db.query(MonitoringLocation).filter_by(id=session.location_id).first()
+        location_name = location.name if location else ""
+        local_start = utc_to_local(session.started_at)
+        session.session_label = _build_session_label(local_start, location_name, session.period_type or "")
+
     if "session_label" in data:
         session.session_label = str(data["session_label"]).strip() or None
     if "period_type" in data:
@@ -1822,8 +2094,111 @@ async def patch_session(
             raise HTTPException(status_code=400, detail=f"Invalid period_type. Must be one of: {', '.join(sorted(VALID_PERIOD_TYPES))}")
         session.period_type = pt or None
 
+    # Configurable period window (0–23 integers; null = no filter)
+    for field in ("period_start_hour", "period_end_hour"):
+        if field in data:
+            val = data[field]
+            if val is None or val == "":
+                setattr(session, field, None)
+            else:
+                try:
+                    h = int(val)
+                    if not (0 <= h <= 23):
+                        raise ValueError
+                    setattr(session, field, h)
+                except (ValueError, TypeError):
+                    raise HTTPException(status_code=400, detail=f"{field} must be an integer 0–23 or null")
+
+    if "report_date" in data:
+        val = data["report_date"]
+        if val is None or val == "":
+            session.report_date = None
+        else:
+            try:
+                from datetime import date as _date
+                session.report_date = _date.fromisoformat(str(val))
+            except ValueError:
+                raise HTTPException(status_code=400, detail="Invalid report_date format. Use YYYY-MM-DD.")
+
     db.commit()
-    return JSONResponse({"status": "success", "session_label": session.session_label, "period_type": session.period_type})
+    return JSONResponse({
+        "status": "success",
+        "session_label": session.session_label,
+        "period_type": session.period_type,
+        "period_start_hour": session.period_start_hour,
+        "period_end_hour": session.period_end_hour,
+        "report_date": session.report_date.isoformat() if session.report_date else None,
+    })
+
+
+@router.get("/{project_id}/sessions/{session_id}/detail", response_class=HTMLResponse)
+async def view_session_detail(
+    request: Request,
+    project_id: str,
+    session_id: str,
+    db: Session = Depends(get_db),
+):
+    """
+    Session detail page: shows files, editable session info, data preview, and report actions.
+    """
+    from backend.models import DataFile
+    from pathlib import Path
+
+    project = db.query(Project).filter_by(id=project_id).first()
+    if not project:
+        raise HTTPException(status_code=404, detail="Project not found")
+    _require_sound_project(project)
+
+    session = db.query(MonitoringSession).filter_by(id=session_id, project_id=project_id).first()
+    if not session:
+        raise HTTPException(status_code=404, detail="Session not found")
+
+    location = db.query(MonitoringLocation).filter_by(id=session.location_id).first() if session.location_id else None
+    unit = db.query(RosterUnit).filter_by(id=session.unit_id).first() if session.unit_id else None
+
+    # Load all data files for this session
+    files = db.query(DataFile).filter_by(session_id=session_id).order_by(DataFile.created_at).all()
+
+    # Compute effective time range string for display
+    effective_range = None
+    if session.period_start_hour is not None and session.period_end_hour is not None and session.started_at:
+        local_start = utc_to_local(session.started_at)
+        start_day = session.report_date if session.report_date else local_start.date()
+        sh = session.period_start_hour
+        eh = session.period_end_hour
+        def _fmt_h(h):
+            ampm = "AM" if h < 12 else "PM"
+            h12 = h % 12 or 12
+            return f"{h12}:00 {ampm}"
+        start_str = f"{start_day.month}/{start_day.day} {_fmt_h(sh)}"
+        if eh > sh:
+            end_day = start_day
+        else:
+            from datetime import timedelta as _td
+            end_day = start_day + _td(days=1)
+        end_str = f"{end_day.month}/{end_day.day} {_fmt_h(eh)}"
+        effective_range = f"{start_str} → {end_str}"
+
+    # Parse session_metadata if present
+    session_meta = {}
+    if session.session_metadata:
+        try:
+            session_meta = json.loads(session.session_metadata)
+        except Exception:
+            pass
+
+    return templates.TemplateResponse("session_detail.html", {
+        "request": request,
+        "project": project,
+        "project_id": project_id,
+        "session": session,
+        "location": location,
+        "unit": unit,
+        "files": files,
+        "effective_range": effective_range,
+        "session_meta": session_meta,
+        "report_date": session.report_date.isoformat() if session.report_date else "",
+    })
 
 
 @router.get("/{project_id}/files/{file_id}/view-rnd", response_class=HTMLResponse)
@@ -1858,6 +2233,7 @@ async def view_rnd_file(
 
     # Get project info
     project = db.query(Project).filter_by(id=project_id).first()
+    _require_sound_project(project)
 
     # Get location info if available
     location = None
@@ -1889,6 +2265,8 @@ async def view_rnd_file(
         "metadata": metadata,
         "filename": file_path.name,
         "is_leq": _is_leq_file(str(file_record.file_path), _peek_rnd_headers(file_path)),
+        "period_start_hour": session.period_start_hour,
+        "period_end_hour": session.period_end_hour,
     })
 
 
@@ -1901,12 +2279,15 @@ async def get_rnd_data(
     """
     Get parsed RND file data as JSON.
     Returns the measurement data for charts and tables.
+    Sound Monitoring projects only.
     """
     from backend.models import DataFile
     from pathlib import Path
     import csv
     import io
 
+    _require_sound_project(db.query(Project).filter_by(id=project_id).first())
+
     # Get the file record
     file_record = db.query(DataFile).filter_by(id=file_id).first()
     if not file_record:
@@ -1995,6 +2376,8 @@ async def get_rnd_data(
             "summary": summary,
             "headers": summary["headers"],
             "data": rows,
+            "period_start_hour": session.period_start_hour,
+            "period_end_hour": session.period_end_hour,
         }
 
     except Exception as e:
@@ -2063,6 +2446,7 @@ async def generate_excel_report(
 
     # Get related data for report context
     project = db.query(Project).filter_by(id=project_id).first()
+    _require_sound_project(project)
     location = db.query(MonitoringLocation).filter_by(id=session.location_id).first() if session.location_id else None
 
     # Build full file path
@@ -2349,7 +2733,7 @@ async def generate_excel_report(
     _plot_border.ln.solidFill = "000000"
     _plot_border.ln.w = 12700
     chart.plot_area.spPr = _plot_border
-    ws.add_chart(chart, "H4")
+    ws.add_chart(chart, "I4")
 
     # --- Stats table: note at I28-I29, headers at I31, data rows 32-34 ---
     note1 = ws.cell(row=28, column=9, value="Note: Averages are calculated by determining the arithmetic average ")
@@ -2493,6 +2877,7 @@ async def preview_report_data(
 
     # Get related data for report context
     project = db.query(Project).filter_by(id=project_id).first()
+    _require_sound_project(project)
     location = db.query(MonitoringLocation).filter_by(id=session.location_id).first() if session.location_id else None
 
     # Build full file path
@@ -2704,6 +3089,7 @@ async def generate_report_from_preview(
         raise HTTPException(status_code=403, detail="File does not belong to this project")
 
     project = db.query(Project).filter_by(id=project_id).first()
+    _require_sound_project(project)
     location = db.query(MonitoringLocation).filter_by(id=session.location_id).first() if session.location_id else None
 
     # Extract data from request
@@ -2835,7 +3221,7 @@ async def generate_report_from_preview(
         _plot_border.ln.solidFill = "000000"
         _plot_border.ln.w = 12700
         chart.plot_area.spPr = _plot_border
-        ws.add_chart(chart, "H4")
+        ws.add_chart(chart, "I4")
 
     # --- Stats block starting at I28 ---
     # Stats table: note at I28-I29, headers at I31, data rows 32-34, border row 35
@@ -2984,6 +3370,7 @@ async def generate_combined_excel_report(
     project = db.query(Project).filter_by(id=project_id).first()
     if not project:
         raise HTTPException(status_code=404, detail="Project not found")
+    _require_sound_project(project)
 
     # Get all sessions with measurement files
     sessions = db.query(MonitoringSession).filter_by(project_id=project_id).all()
@@ -3182,7 +3569,7 @@ async def generate_combined_excel_report(
         _plot_border.ln.solidFill = "000000"
         _plot_border.ln.w = 12700
         chart.plot_area.spPr = _plot_border
-        ws.add_chart(chart, "H4")
+        ws.add_chart(chart, "I4")
 
         # Stats table: note at I28-I29, headers at I31, data rows 32-34, border row 35
         note1 = ws.cell(row=28, column=9, value="Note: Averages are calculated by determining the arithmetic average ")
@@ -3329,6 +3716,7 @@ async def combined_report_wizard(
     project = db.query(Project).filter_by(id=project_id).first()
     if not project:
         raise HTTPException(status_code=404, detail="Project not found")
+    _require_sound_project(project)
 
     sessions = db.query(MonitoringSession).filter_by(project_id=project_id).order_by(MonitoringSession.started_at).all()
 
@@ -3421,7 +3809,10 @@ def _build_location_data_from_sessions(project_id: str, db, selected_session_ids
             "loc_name": loc_name,
             "session_label": session.session_label or "",
             "period_type": session.period_type or "",
+            "period_start_hour": session.period_start_hour,
+            "period_end_hour": session.period_end_hour,
             "started_at": session.started_at,
+            "report_date": session.report_date,
             "rows": [],
         }
 
@@ -3462,25 +3853,39 @@ def _build_location_data_from_sessions(project_id: str, db, selected_session_ids
                     pass
             parsed.append((dt, row))
 
-        # Determine which rows to keep based on period_type
-        is_day_session = period_type in ('weekday_day', 'weekend_day')
+        # Determine effective hour window.
+        # Prefer per-session period_start/end_hour; fall back to hardcoded defaults.
+        sh = entry.get("period_start_hour")  # e.g. 7 for Day, 19 for Night
+        eh = entry.get("period_end_hour")    # e.g. 19 for Day,  7 for Night
+        if sh is None or eh is None:
+            # Legacy defaults based on period_type
+            is_day_session = period_type in ('weekday_day', 'weekend_day')
+            sh = 7 if is_day_session else 19
+            eh = 19 if is_day_session else 7
+        else:
+            is_day_session = eh > sh  # crosses midnight when end < start
+
         target_date = None
         if is_day_session:
-            # Day: 07:00–18:59 only, restricted to the LAST calendar date that has daytime rows
-            daytime_dates = sorted({
-                dt.date() for dt, row in parsed
-                if dt and 7 <= dt.hour < 19
-            })
-            target_date = daytime_dates[-1] if daytime_dates else None
+            # Day-style: start_h <= hour < end_h, restricted to the LAST calendar date
+            in_window = lambda h: sh <= h < eh
+            if entry.get("report_date"):
+                target_date = entry["report_date"]
+            else:
+                daytime_dates = sorted({
+                    dt.date() for dt, row in parsed if dt and in_window(dt.hour)
+                })
+                target_date = daytime_dates[-1] if daytime_dates else None
             filtered = [
                 (dt, row) for dt, row in parsed
-                if dt and dt.date() == target_date and 7 <= dt.hour < 19
+                if dt and dt.date() == target_date and in_window(dt.hour)
             ]
         else:
-            # Night: 19:00–06:59, spanning both calendar days — no date restriction
+            # Night-style: hour >= start_h OR hour < end_h (crosses midnight)
+            in_window = lambda h: h >= sh or h < eh
             filtered = [
                 (dt, row) for dt, row in parsed
-                if dt and (dt.hour >= 19 or dt.hour < 7)
+                if dt and in_window(dt.hour)
             ]
 
         # Fall back to all rows if filtering removed everything
@@ -3598,6 +4003,7 @@ async def generate_combined_from_preview(
     project = db.query(Project).filter_by(id=project_id).first()
     if not project:
         raise HTTPException(status_code=404, detail="Project not found")
+    _require_sound_project(project)
 
     report_title = data.get("report_title", "Background Noise Study")
     project_name = data.get("project_name", project.name)
@@ -3760,7 +4166,7 @@ async def generate_combined_from_preview(
         _plot_border.ln.solidFill = "000000"
         _plot_border.ln.w = 12700
         chart.plot_area.spPr = _plot_border
-        ws.add_chart(chart, "H4")
+        ws.add_chart(chart, "I4")
 
         hdr_fill_tbl = PatternFill(start_color="F2F2F2", end_color="F2F2F2", fill_type="solid")
 
@@ -4073,6 +4479,7 @@ async def upload_all_project_data(
     project = db.query(Project).filter_by(id=project_id).first()
     if not project:
         raise HTTPException(status_code=404, detail="Project not found")
+    _require_sound_project(project)
 
     # Load all sound monitoring locations for this project
     locations = db.query(MonitoringLocation).filter_by(
diff --git a/backend/templates_config.py b/backend/templates_config.py
index d1c7360..96a871f 100644
--- a/backend/templates_config.py
+++ b/backend/templates_config.py
@@ -73,10 +73,16 @@ def jinja_log_tail_display(s):
         return str(s)
 
 
+def jinja_local_datetime_input(dt):
+    """Jinja filter: format UTC datetime as local YYYY-MM-DDTHH:MM for <input type='datetime-local'>."""
+    return format_local_datetime(dt, "%Y-%m-%dT%H:%M")
+
+
 # Register Jinja filters and globals
 templates.env.filters["local_datetime"] = jinja_local_datetime
 templates.env.filters["local_time"] = jinja_local_time
 templates.env.filters["local_date"] = jinja_local_date
+templates.env.filters["local_datetime_input"] = jinja_local_datetime_input
 templates.env.filters["fromjson"] = jinja_fromjson
 templates.env.globals["timezone_abbr"] = jinja_timezone_abbr
 templates.env.globals["get_user_timezone"] = get_user_timezone
diff --git a/templates/partials/projects/session_list.html b/templates/partials/projects/session_list.html
index 6b8b617..2886855 100644
--- a/templates/partials/projects/session_list.html
+++ b/templates/partials/projects/session_list.html
@@ -5,6 +5,7 @@
         {% set s = item.session %}
         {% set loc = item.location %}
         {% set unit = item.unit %}
+        {% set effective_range = item.effective_range %}
 
         {# Period display maps #}
         {% set period_labels = {
@@ -49,25 +50,74 @@
                             <span class="px-2 py-0.5 text-xs font-medium bg-gray-100 text-gray-600 dark:bg-gray-700 dark:text-gray-400 rounded-full">Failed</span>
                         {% endif %}
 
-                        <!-- Period type badge (click to change) -->
+                        <!-- Period type badge (click to open hour editor) -->
                         <div class="relative" id="period-wrap-{{ s.id }}">
-                            <button onclick="togglePeriodMenu('{{ s.id }}')"
+                            <button onclick="openPeriodEditor('{{ s.id }}')"
                                     id="period-badge-{{ s.id }}"
                                     class="px-2 py-0.5 text-xs font-medium rounded-full flex items-center gap-1 transition-colors {{ period_colors.get(s.period_type, 'bg-gray-100 text-gray-500 dark:bg-gray-700 dark:text-gray-400') }}"
-                                    title="Click to change period type">
+                                    title="Click to edit period type and hours">
                                 <span id="period-label-{{ s.id }}">{{ period_labels.get(s.period_type, 'Set period') }}</span>
                                 <svg class="w-3 h-3 opacity-60 shrink-0" fill="none" stroke="currentColor" viewBox="0 0 24 24">
                                     <path stroke-linecap="round" stroke-linejoin="round" stroke-width="2" d="M19 9l-7 7-7-7"></path>
                                 </svg>
                             </button>
-                            <div id="period-menu-{{ s.id }}"
-                                 class="hidden absolute left-0 top-full mt-1 z-20 bg-white dark:bg-slate-700 border border-gray-200 dark:border-gray-600 rounded-lg shadow-lg min-w-[160px] py-1">
-                                {% for pt, pt_label in [('weekday_day','Weekday Day'),('weekday_night','Weekday Night'),('weekend_day','Weekend Day'),('weekend_night','Weekend Night')] %}
-                                <button onclick="setPeriodType('{{ s.id }}', '{{ pt }}')"
-                                        class="w-full text-left px-3 py-1.5 text-xs hover:bg-gray-100 dark:hover:bg-slate-600 text-gray-700 dark:text-gray-300 {% if s.period_type == pt %}font-bold{% endif %}">
-                                    {{ pt_label }}
-                                </button>
-                                {% endfor %}
+
+                            <!-- Period editor panel -->
+                            <div id="period-editor-{{ s.id }}"
+                                 class="hidden absolute left-0 top-full mt-1 z-20 bg-white dark:bg-slate-700 border border-gray-200 dark:border-gray-600 rounded-lg shadow-lg w-64 p-3 space-y-3">
+
+                                <!-- Period type selector -->
+                                <div>
+                                    <label class="block text-xs font-medium text-gray-600 dark:text-gray-400 mb-1">Period Type</label>
+                                    <div class="grid grid-cols-2 gap-1">
+                                        {% for pt, pt_label in [('weekday_day','WD Day'),('weekday_night','WD Night'),('weekend_day','WE Day'),('weekend_night','WE Night')] %}
+                                        <button onclick="selectPeriodType('{{ s.id }}', '{{ pt }}')"
+                                                id="pt-btn-{{ s.id }}-{{ pt }}"
+                                                class="period-type-btn text-xs py-1 px-2 rounded border transition-colors
+                                                       {% if s.period_type == pt %}border-seismo-orange bg-orange-50 text-seismo-orange dark:bg-orange-900/20{% else %}border-gray-200 dark:border-gray-600 text-gray-600 dark:text-gray-400 hover:border-gray-400{% endif %}">
+                                            {{ pt_label }}
+                                        </button>
+                                        {% endfor %}
+                                    </div>
+                                </div>
+
+                                <!-- Hour inputs -->
+                                <div class="grid grid-cols-2 gap-2">
+                                    <div>
+                                        <label class="block text-xs text-gray-500 dark:text-gray-400 mb-1">Start Hour (0–23)</label>
+                                        <input type="number" min="0" max="23"
+                                               id="period-start-hr-{{ s.id }}"
+                                               value="{{ s.period_start_hour if s.period_start_hour is not none else '' }}"
+                                               placeholder="e.g. 19"
+                                               class="w-full text-xs bg-gray-50 dark:bg-slate-600 border border-gray-200 dark:border-gray-500 rounded px-2 py-1 text-gray-800 dark:text-gray-200 focus:outline-none focus:border-seismo-orange">
+                                    </div>
+                                    <div>
+                                        <label class="block text-xs text-gray-500 dark:text-gray-400 mb-1">End Hour (0–23)</label>
+                                        <input type="number" min="0" max="23"
+                                               id="period-end-hr-{{ s.id }}"
+                                               value="{{ s.period_end_hour if s.period_end_hour is not none else '' }}"
+                                               placeholder="e.g. 7"
+                                               class="w-full text-xs bg-gray-50 dark:bg-slate-600 border border-gray-200 dark:border-gray-500 rounded px-2 py-1 text-gray-800 dark:text-gray-200 focus:outline-none focus:border-seismo-orange">
+                                    </div>
+                                </div>
+                                <p class="text-xs text-gray-400 dark:text-gray-500">Day: 7→19 · Night: 19→7 · Customize as needed</p>
+
+                                <!-- Actions -->
+                                <div class="flex gap-2 pt-1">
+                                    <button onclick="savePeriodEditor('{{ s.id }}')"
+                                            class="flex-1 text-xs py-1 bg-seismo-orange text-white rounded hover:bg-orange-600 transition-colors">
+                                        Save
+                                    </button>
+                                    <button onclick="closePeriodEditor('{{ s.id }}')"
+                                            class="text-xs py-1 px-2 border border-gray-200 dark:border-gray-600 rounded text-gray-600 dark:text-gray-400 hover:bg-gray-100 dark:hover:bg-slate-600 transition-colors">
+                                        Cancel
+                                    </button>
+                                    <button onclick="clearPeriodEditor('{{ s.id }}')"
+                                            class="text-xs py-1 px-2 border border-gray-200 dark:border-gray-600 rounded text-gray-500 dark:text-gray-500 hover:bg-gray-100 dark:hover:bg-slate-600 transition-colors"
+                                            title="Clear period type and hours">
+                                        Clear
+                                    </button>
+                                </div>
                             </div>
                         </div>
                     </div>
@@ -131,8 +181,17 @@
                         {% endif %}
                     </div>
 
-                    {% if s.notes %}
-                    <p class="text-xs text-gray-400 dark:text-gray-500 mt-2 italic">{{ s.notes }}</p>
+                    <!-- Effective window (when period hours are set) -->
+                    {% if effective_range %}
+                    <div class="flex items-center gap-1 mt-1.5 text-xs text-indigo-600 dark:text-indigo-400">
+                        <svg class="w-3.5 h-3.5 shrink-0" fill="none" stroke="currentColor" viewBox="0 0 24 24">
+                            <path stroke-linecap="round" stroke-linejoin="round" stroke-width="2" d="M12 8v4l3 3m6-3a9 9 0 11-18 0 9 9 0 0118 0z"></path>
+                        </svg>
+                        <span id="effective-range-{{ s.id }}">Effective: {{ effective_range }}</span>
+                    </div>
+                    {% else %}
+                    <div class="hidden text-xs text-indigo-600 dark:text-indigo-400 mt-1.5"
+                         id="effective-range-{{ s.id }}"></div>
                     {% endif %}
                 </div>
 
@@ -163,6 +222,8 @@
 {% endif %}
 
 <script>
+const PROJECT_ID = '{{ project_id }}';
+
 const PERIOD_COLORS = {
     weekday_day:   'bg-blue-100 text-blue-800 dark:bg-blue-900/30 dark:text-blue-300',
     weekday_night: 'bg-indigo-100 text-indigo-800 dark:bg-indigo-900/30 dark:text-indigo-300',
@@ -175,46 +236,145 @@ const PERIOD_LABELS = {
     weekend_day:   'Weekend Day',
     weekend_night: 'Weekend Night',
 };
+// Default hours for each period type
+const PERIOD_DEFAULT_HOURS = {
+    weekday_day:   {start: 7,  end: 19},
+    weekday_night: {start: 19, end: 7},
+    weekend_day:   {start: 7,  end: 19},
+    weekend_night: {start: 19, end: 7},
+};
 const FALLBACK_COLORS = ['bg-gray-100','text-gray-500','dark:bg-gray-700','dark:text-gray-400'];
 const ALL_BADGE_COLORS = [...new Set([
     ...FALLBACK_COLORS,
     ...Object.values(PERIOD_COLORS).flatMap(s => s.split(' '))
 ])];
 
-function togglePeriodMenu(sessionId) {
-    const menu = document.getElementById('period-menu-' + sessionId);
-    document.querySelectorAll('[id^="period-menu-"]').forEach(m => {
-        if (m.id !== 'period-menu-' + sessionId) m.classList.add('hidden');
+// Track which period type is selected in the editor before saving
+const _editorState = {};
+
+// ---- Period editor ----
+
+function openPeriodEditor(sessionId) {
+    // Close all other editors first
+    document.querySelectorAll('[id^="period-editor-"]').forEach(el => {
+        if (el.id !== 'period-editor-' + sessionId) el.classList.add('hidden');
     });
-    menu.classList.toggle('hidden');
+    document.getElementById('period-editor-' + sessionId).classList.toggle('hidden');
 }
 
+function closePeriodEditor(sessionId) {
+    document.getElementById('period-editor-' + sessionId).classList.add('hidden');
+    delete _editorState[sessionId];
+}
+
+function selectPeriodType(sessionId, pt) {
+    _editorState[sessionId] = pt;
+    // Highlight selected button
+    document.querySelectorAll(`[id^="pt-btn-${sessionId}-"]`).forEach(btn => {
+        const isSelected = btn.id === `pt-btn-${sessionId}-${pt}`;
+        btn.classList.toggle('border-seismo-orange', isSelected);
+        btn.classList.toggle('bg-orange-50', isSelected);
+        btn.classList.toggle('text-seismo-orange', isSelected);
+        btn.classList.toggle('dark:bg-orange-900/20', isSelected);
+        btn.classList.toggle('border-gray-200', !isSelected);
+        btn.classList.toggle('dark:border-gray-600', !isSelected);
+        btn.classList.toggle('text-gray-600', !isSelected);
+        btn.classList.toggle('dark:text-gray-400', !isSelected);
+    });
+    // Fill default hours
+    const defaults = PERIOD_DEFAULT_HOURS[pt];
+    if (defaults) {
+        const sh = document.getElementById('period-start-hr-' + sessionId);
+        const eh = document.getElementById('period-end-hr-' + sessionId);
+        if (sh && !sh.value) sh.value = defaults.start;
+        if (eh && !eh.value) eh.value = defaults.end;
+    }
+}
+
+async function savePeriodEditor(sessionId) {
+    const pt = _editorState[sessionId] || document.getElementById('period-badge-' + sessionId)
+                                           ?.dataset?.currentPeriod || null;
+    const shInput = document.getElementById('period-start-hr-' + sessionId);
+    const ehInput = document.getElementById('period-end-hr-' + sessionId);
+
+    const payload = {};
+    if (pt !== undefined) payload.period_type = pt || null;
+    payload.period_start_hour = shInput?.value !== '' ? parseInt(shInput.value, 10) : null;
+    payload.period_end_hour   = ehInput?.value !== '' ? parseInt(ehInput.value, 10) : null;
+
+    try {
+        const resp = await fetch(`/api/projects/${PROJECT_ID}/sessions/${sessionId}`, {
+            method: 'PATCH',
+            headers: {'Content-Type': 'application/json'},
+            body: JSON.stringify(payload),
+        });
+        if (!resp.ok) throw new Error(await resp.text());
+        const result = await resp.json();
+
+        // Update badge
+        const badge = document.getElementById('period-badge-' + sessionId);
+        const label = document.getElementById('period-label-' + sessionId);
+        const newPt = result.period_type;
+        ALL_BADGE_COLORS.forEach(c => badge.classList.remove(c));
+        if (newPt && PERIOD_COLORS[newPt]) {
+            badge.classList.add(...PERIOD_COLORS[newPt].split(' ').filter(Boolean));
+            if (label) label.textContent = PERIOD_LABELS[newPt];
+        } else {
+            badge.classList.add(...FALLBACK_COLORS);
+            if (label) label.textContent = 'Set period';
+        }
+
+        // Update effective range display
+        _updateEffectiveRange(sessionId, result.period_start_hour, result.period_end_hour);
+
+        closePeriodEditor(sessionId);
+    } catch (err) {
+        alert('Failed to save period: ' + err.message);
+    }
+}
+
+async function clearPeriodEditor(sessionId) {
+    const shInput = document.getElementById('period-start-hr-' + sessionId);
+    const ehInput = document.getElementById('period-end-hr-' + sessionId);
+    if (shInput) shInput.value = '';
+    if (ehInput) ehInput.value = '';
+    _editorState[sessionId] = null;
+
+    // Reset period type button highlights
+    document.querySelectorAll(`[id^="pt-btn-${sessionId}-"]`).forEach(btn => {
+        btn.classList.remove('border-seismo-orange','bg-orange-50','text-seismo-orange','dark:bg-orange-900/20');
+        btn.classList.add('border-gray-200','dark:border-gray-600','text-gray-600','dark:text-gray-400');
+    });
+}
+
+// ---- Effective range helper ----
+
+function _updateEffectiveRange(sessionId, startHour, endHour) {
+    const el = document.getElementById('effective-range-' + sessionId);
+    if (!el) return;
+    if (startHour == null || endHour == null) {
+        el.textContent = '';
+        el.classList.add('hidden');
+        return;
+    }
+    function _fmt(h) {
+        const ampm = h < 12 ? 'AM' : 'PM';
+        const h12 = h % 12 || 12;
+        return `${h12}:00 ${ampm}`;
+    }
+    // We don't have the session start date in JS so just show the hours pattern
+    el.textContent = `Effective window: ${_fmt(startHour)} → ${_fmt(endHour)}`;
+    el.classList.remove('hidden');
+}
+
+// ---- Close editors on outside click ----
 document.addEventListener('click', function(e) {
     if (!e.target.closest('[id^="period-wrap-"]')) {
-        document.querySelectorAll('[id^="period-menu-"]').forEach(m => m.classList.add('hidden'));
+        document.querySelectorAll('[id^="period-editor-"]').forEach(m => m.classList.add('hidden'));
     }
 });
 
-async function setPeriodType(sessionId, periodType) {
-    document.getElementById('period-menu-' + sessionId).classList.add('hidden');
-    const badge = document.getElementById('period-badge-' + sessionId);
-    badge.disabled = true;
-    try {
-        const resp = await fetch(`/api/projects/{{ project_id }}/sessions/${sessionId}`, {
-            method: 'PATCH',
-            headers: {'Content-Type': 'application/json'},
-            body: JSON.stringify({period_type: periodType}),
-        });
-        if (!resp.ok) throw new Error(await resp.text());
-        ALL_BADGE_COLORS.forEach(c => badge.classList.remove(c));
-        badge.classList.add(...(PERIOD_COLORS[periodType] || FALLBACK_COLORS.join(' ')).split(' ').filter(Boolean));
-        document.getElementById('period-label-' + sessionId).textContent = PERIOD_LABELS[periodType] || periodType;
-    } catch(err) {
-        alert('Failed to update period type: ' + err.message);
-    } finally {
-        badge.disabled = false;
-    }
-}
+// ---- Label editing ----
 
 function startEditLabel(sessionId) {
     document.getElementById('label-display-' + sessionId).classList.add('hidden');
@@ -234,7 +394,7 @@ async function saveLabel(sessionId) {
     const input   = document.getElementById('label-input-' + sessionId);
     const newLabel = input.value.trim();
     try {
-        const resp = await fetch(`/api/projects/{{ project_id }}/sessions/${sessionId}`, {
+        const resp = await fetch(`/api/projects/${PROJECT_ID}/sessions/${sessionId}`, {
             method: 'PATCH',
             headers: {'Content-Type': 'application/json'},
             body: JSON.stringify({session_label: newLabel}),
@@ -249,8 +409,10 @@ async function saveLabel(sessionId) {
     }
 }
 
+// ---- Session details ----
+
 function viewSession(sessionId) {
-    alert('Session details coming soon: ' + sessionId);
+    window.location.href = `/api/projects/${PROJECT_ID}/sessions/${sessionId}/detail`;
 }
 
 function stopRecording(sessionId) {
diff --git a/templates/partials/projects/sessions_calendar.html b/templates/partials/projects/sessions_calendar.html
new file mode 100644
index 0000000..fc29eea
--- /dev/null
+++ b/templates/partials/projects/sessions_calendar.html
@@ -0,0 +1,124 @@
+<!-- Monthly Sessions Calendar — Gantt Style -->
+<div class="sessions-cal-wrap bg-white dark:bg-slate-800 rounded-xl border border-gray-200 dark:border-gray-700 overflow-hidden">
+
+    <!-- Month navigation -->
+    <div class="px-5 py-3 border-b border-gray-200 dark:border-gray-700 flex items-center justify-between">
+        <button hx-get="/api/projects/{{ project_id }}/sessions-calendar?month={{ prev_month }}&year={{ prev_year }}"
+                hx-target="#sessions-calendar"
+                hx-swap="innerHTML"
+                class="p-1.5 rounded-lg hover:bg-gray-100 dark:hover:bg-slate-700 transition-colors text-gray-500 dark:text-gray-400"
+                title="Previous month">
+            <svg class="w-4 h-4" fill="none" stroke="currentColor" viewBox="0 0 24 24">
+                <path stroke-linecap="round" stroke-linejoin="round" stroke-width="2" d="M15 19l-7-7 7-7"></path>
+            </svg>
+        </button>
+        <h3 class="text-sm font-semibold text-gray-800 dark:text-gray-200">{{ month_name }} {{ year }}</h3>
+        <button hx-get="/api/projects/{{ project_id }}/sessions-calendar?month={{ next_month }}&year={{ next_year }}"
+                hx-target="#sessions-calendar"
+                hx-swap="innerHTML"
+                class="p-1.5 rounded-lg hover:bg-gray-100 dark:hover:bg-slate-700 transition-colors text-gray-500 dark:text-gray-400"
+                title="Next month">
+            <svg class="w-4 h-4" fill="none" stroke="currentColor" viewBox="0 0 24 24">
+                <path stroke-linecap="round" stroke-linejoin="round" stroke-width="2" d="M9 5l7 7-7 7"></path>
+            </svg>
+        </button>
+    </div>
+
+    <!-- Legend + key -->
+    <div class="px-5 py-2 border-b border-gray-100 dark:border-gray-700 flex flex-wrap items-center gap-x-5 gap-y-1.5">
+        {% if legend %}
+        <div class="flex flex-wrap gap-x-4 gap-y-1">
+            {% for loc in legend %}
+            <div class="flex items-center gap-1.5 text-xs text-gray-600 dark:text-gray-400">
+                <span class="w-2.5 h-2.5 rounded-full shrink-0" style="background-color: {{ loc.color }}"></span>
+                <span>{{ loc.name }}</span>
+            </div>
+            {% endfor %}
+        </div>
+        {% endif %}
+        <!-- Bar key -->
+        <div class="flex items-center gap-3 text-xs text-gray-400 dark:text-gray-500 ml-auto shrink-0">
+            <div class="flex items-center gap-1.5">
+                <div class="w-8 h-2 rounded-sm" style="background:rgba(100,100,100,0.25)"></div>
+                <span>Device on</span>
+            </div>
+            <div class="flex items-center gap-1.5">
+                <div class="w-8 h-2 rounded-sm bg-blue-500"></div>
+                <span>Effective window</span>
+            </div>
+        </div>
+    </div>
+
+    <!-- Day-of-week headers -->
+    <div class="grid grid-cols-7 border-b border-gray-100 dark:border-gray-700">
+        {% for day_name in ['Sun', 'Mon', 'Tue', 'Wed', 'Thu', 'Fri', 'Sat'] %}
+        <div class="py-2 text-center text-xs font-medium uppercase tracking-wide
+                    {% if loop.index == 1 or loop.index == 7 %}text-amber-500 dark:text-amber-400{% else %}text-gray-400 dark:text-gray-500{% endif %}">
+            {{ day_name }}
+        </div>
+        {% endfor %}
+    </div>
+
+    <!-- Calendar grid -->
+    {% for week in weeks %}
+    <div class="grid grid-cols-7 {% if not loop.last %}border-b border-gray-100 dark:border-gray-700{% endif %}">
+        {% for day in week %}
+        <div class="min-h-[80px] p-1.5
+                    {% if not loop.last %}border-r border-gray-100 dark:border-gray-700{% endif %}
+                    {% if not day.in_month %}bg-gray-50 dark:bg-slate-800/50{% else %}bg-white dark:bg-slate-800{% endif %}
+                    {% if day.is_today %}ring-1 ring-inset ring-seismo-orange{% endif %}">
+
+            <!-- Date number -->
+            <div class="text-right mb-1.5">
+                <span class="text-xs {% if day.is_today %}font-bold text-seismo-orange{% elif day.in_month %}text-gray-700 dark:text-gray-300{% else %}text-gray-300 dark:text-gray-600{% endif %}">
+                    {{ day.date.day }}
+                </span>
+            </div>
+
+            <!-- Gantt bars -->
+            {% if day.sessions %}
+            <div class="space-y-2">
+                {% for s in day.sessions %}
+
+                <a href="/api/projects/{{ project_id }}/sessions/{{ s.session_id }}/detail" class="block">
+
+                    <!-- 24-hour timeline bar -->
+                    <div class="relative overflow-hidden -mx-1.5" style="height:11px; background:rgba(128,128,128,0.08);">
+                        <div class="absolute top-0 bottom-0 w-px" style="left:25%; background:rgba(128,128,128,0.18)"></div>
+                        <div class="absolute top-0 bottom-0 w-px" style="left:50%; background:rgba(128,128,128,0.28)"></div>
+                        <div class="absolute top-0 bottom-0 w-px" style="left:75%; background:rgba(128,128,128,0.18)"></div>
+                        <div class="absolute top-0 bottom-0"
+                             style="left:{{ s.dev_start_pct }}%; width:{{ s.dev_width_pct }}%; background-color:{{ s.color }}; opacity:0.28;"></div>
+                        {% if s.eff_start_pct is not none %}
+                        <div class="absolute"
+                             style="left:{{ s.eff_start_pct }}%; width:{{ s.eff_width_pct }}%; top:1.5px; bottom:1.5px; background-color:{{ s.color }};"></div>
+                        {% endif %}
+                    </div>
+
+                    <!-- Label -->
+                    <div class="truncate mt-0.5" style="color:{{ s.color }}; font-size:0.58rem; line-height:1.3;">
+                        {{ s.location_name }} · {{ day.date.strftime('%-m/%-d') }} · {% if s.period_type %}{{ 'Night' if 'night' in s.period_type else 'Day' }}{% else %}—{% endif %}
+                    </div>
+
+                </a>
+
+                {% endfor %}
+            </div>
+            {% endif %}
+
+        </div>
+        {% endfor %}
+    </div>
+    {% endfor %}
+
+    <!-- Time scale footer hint -->
+    <div class="px-4 py-1.5 border-t border-gray-100 dark:border-gray-700 flex justify-between text-gray-300 dark:text-gray-600" style="font-size:0.6rem;">
+        <span>12 AM</span>
+        <span>6 AM</span>
+        <span>12 PM</span>
+        <span>6 PM</span>
+        <span>12 AM</span>
+    </div>
+
+</div>
+
diff --git a/templates/partials/projects/unified_files.html b/templates/partials/projects/unified_files.html
index 118c217..a3bf0d1 100644
--- a/templates/partials/projects/unified_files.html
+++ b/templates/partials/projects/unified_files.html
@@ -56,6 +56,15 @@
                             {% else %}bg-gray-100 text-gray-800 dark:bg-gray-700 dark:text-gray-300{% endif %}">
                             {{ session.status or 'unknown' }}
                         </span>
+                        <!-- Edit Session Times -->
+                        <button onclick="event.stopPropagation(); openEditSessionModal('{{ session.id }}', '{{ session.started_at|local_datetime if session.started_at else '' }}', '{{ session.stopped_at|local_datetime if session.stopped_at else '' }}')"
+                                class="px-3 py-1 text-xs bg-gray-600 text-white rounded-lg hover:bg-gray-700 transition-colors flex items-center gap-1"
+                                title="Edit session times">
+                            <svg class="w-4 h-4" fill="none" stroke="currentColor" viewBox="0 0 24 24">
+                                <path stroke-linecap="round" stroke-linejoin="round" stroke-width="2" d="M11 5H6a2 2 0 00-2 2v11a2 2 0 002 2h11a2 2 0 002-2v-5m-1.414-9.414a2 2 0 112.828 2.828L11.828 15H9v-2.828l8.586-8.586z"></path>
+                            </svg>
+                            Edit
+                        </button>
                         <!-- Download All Files in Session -->
                         <button onclick="event.stopPropagation(); downloadSessionFiles('{{ session.id }}')"
                                 class="px-3 py-1 text-xs bg-seismo-orange text-white rounded-lg hover:bg-seismo-navy transition-colors flex items-center gap-1"
@@ -326,4 +335,74 @@ async function deleteSession(sessionId) {
         alert(`Error deleting session: ${error.message}`);
     }
 }
+
+function openEditSessionModal(sessionId, startedAt, stoppedAt) {
+    document.getElementById('editSessionId').value = sessionId;
+    // local_datetime filter returns "YYYY-MM-DD HH:MM" — convert to "YYYY-MM-DDTHH:MM" for datetime-local input
+    document.getElementById('editStartedAt').value = startedAt ? startedAt.replace(' ', 'T') : '';
+    document.getElementById('editStoppedAt').value = stoppedAt ? stoppedAt.replace(' ', 'T') : '';
+    document.getElementById('editSessionModal').classList.remove('hidden');
+}
+
+function closeEditSessionModal() {
+    document.getElementById('editSessionModal').classList.add('hidden');
+}
+
+async function saveSessionTimes() {
+    const sessionId = document.getElementById('editSessionId').value;
+    const startedAt = document.getElementById('editStartedAt').value;
+    const stoppedAt = document.getElementById('editStoppedAt').value;
+
+    try {
+        const response = await fetch(`/api/projects/{{ project_id }}/sessions/${sessionId}`, {
+            method: 'PATCH',
+            headers: {'Content-Type': 'application/json'},
+            body: JSON.stringify({
+                started_at: startedAt || null,
+                stopped_at: stoppedAt || null,
+            })
+        });
+
+        if (response.ok) {
+            closeEditSessionModal();
+            window.location.reload();
+        } else {
+            const data = await response.json();
+            alert(`Failed to update session: ${data.detail || 'Unknown error'}`);
+        }
+    } catch (error) {
+        alert(`Error updating session: ${error.message}`);
+    }
+}
 </script>
+
+<!-- Edit Session Times Modal -->
+<div id="editSessionModal" class="hidden fixed inset-0 z-50 flex items-center justify-center bg-black/50">
+    <div class="bg-white dark:bg-gray-800 rounded-xl shadow-xl p-6 w-full max-w-sm mx-4">
+        <h3 class="text-lg font-semibold text-gray-900 dark:text-white mb-4">Edit Session Times</h3>
+        <input type="hidden" id="editSessionId">
+        <div class="space-y-4">
+            <div>
+                <label class="block text-sm font-medium text-gray-700 dark:text-gray-300 mb-1">Start Time</label>
+                <input type="datetime-local" id="editStartedAt"
+                       class="w-full px-3 py-2 border border-gray-300 dark:border-gray-600 rounded-lg bg-white dark:bg-gray-700 text-gray-900 dark:text-white text-sm focus:outline-none focus:ring-2 focus:ring-blue-500">
+            </div>
+            <div>
+                <label class="block text-sm font-medium text-gray-700 dark:text-gray-300 mb-1">Stop Time</label>
+                <input type="datetime-local" id="editStoppedAt"
+                       class="w-full px-3 py-2 border border-gray-300 dark:border-gray-600 rounded-lg bg-white dark:bg-gray-700 text-gray-900 dark:text-white text-sm focus:outline-none focus:ring-2 focus:ring-blue-500">
+            </div>
+        </div>
+        <p class="mt-3 text-xs text-gray-500 dark:text-gray-400">Times are in your local timezone. The session label and period type will be updated automatically.</p>
+        <div class="flex justify-end gap-3 mt-5">
+            <button onclick="closeEditSessionModal()"
+                    class="px-4 py-2 text-sm text-gray-700 dark:text-gray-300 bg-gray-100 dark:bg-gray-700 rounded-lg hover:bg-gray-200 dark:hover:bg-gray-600 transition-colors">
+                Cancel
+            </button>
+            <button onclick="saveSessionTimes()"
+                    class="px-4 py-2 text-sm text-white bg-blue-600 rounded-lg hover:bg-blue-700 transition-colors">
+                Save
+            </button>
+        </div>
+    </div>
+</div>
diff --git a/templates/projects/detail.html b/templates/projects/detail.html
index 5a4a8cf..e3131dc 100644
--- a/templates/projects/detail.html
+++ b/templates/projects/detail.html
@@ -208,6 +208,19 @@
                 <div class="text-center py-8 text-gray-500">Loading sessions...</div>
             </div>
         </div>
+
+        <!-- Monthly Calendar -->
+        <div class="mt-6 bg-white dark:bg-slate-800 rounded-xl shadow-lg p-6">
+            <div class="flex items-center justify-between mb-4">
+                <h3 class="text-lg font-semibold text-gray-900 dark:text-white">Calendar View</h3>
+            </div>
+            <div id="sessions-calendar"
+                 hx-get="/api/projects/{{ project_id }}/sessions-calendar"
+                 hx-trigger="load"
+                 hx-swap="innerHTML">
+                <div class="text-center py-6 text-gray-400 text-sm">Loading calendar…</div>
+            </div>
+        </div>
     </div>
 
     <!-- Data Files Tab -->
@@ -838,6 +851,7 @@ async function loadProjectDetails() {
 
         // Update tab labels and visibility based on project type
         const isSoundProject = projectTypeId === 'sound_monitoring';
+        const isVibrationProject = projectTypeId === 'vibration_monitoring';
         if (isSoundProject) {
             document.getElementById('locations-tab-label').textContent = 'NRLs';
             document.getElementById('locations-header').textContent = 'Noise Recording Locations';
@@ -848,9 +862,9 @@ async function loadProjectDetails() {
         const isRemote = mode === 'remote';
         document.getElementById('sessions-tab-btn').classList.toggle('hidden', !isSoundProject);
         document.getElementById('data-tab-btn').classList.toggle('hidden', !isSoundProject);
-        // Schedules and Assigned Units are remote-only (manual projects collect data by hand)
-        document.getElementById('schedules-tab-btn')?.classList.toggle('hidden', isSoundProject && !isRemote);
-        document.getElementById('units-tab-btn')?.classList.toggle('hidden', isSoundProject && !isRemote);
+        // Schedules and Assigned Units: hidden for vibration; for sound, only show if remote
+        document.getElementById('schedules-tab-btn')?.classList.toggle('hidden', isVibrationProject || (isSoundProject && !isRemote));
+        document.getElementById('units-tab-btn')?.classList.toggle('hidden', isVibrationProject || (isSoundProject && !isRemote));
         // FTP browser within Data Files tab
         document.getElementById('ftp-browser')?.classList.toggle('hidden', !isRemote);
 
@@ -1828,5 +1842,6 @@ document.addEventListener('DOMContentLoaded', function() {
         switchTab(hash);
     }
 });
+
 </script>
 {% endblock %}
diff --git a/templates/rnd_viewer.html b/templates/rnd_viewer.html
index 95ca840..507c3f8 100644
--- a/templates/rnd_viewer.html
+++ b/templates/rnd_viewer.html
@@ -181,6 +181,27 @@ let chartInstance = null;
 let allData = [];
 let allHeaders = [];
 
+// Session period window (null = no filtering)
+const SESSION_PERIOD_START_HOUR = {{ period_start_hour if period_start_hour is not none else 'null' }};
+const SESSION_PERIOD_END_HOUR   = {{ period_end_hour if period_end_hour is not none else 'null' }};
+
+/**
+ * Returns true if the given hour integer is within the session's period window.
+ * Always returns true when no period window is configured.
+ */
+function _isInPeriodWindow(hour) {
+    if (SESSION_PERIOD_START_HOUR === null || SESSION_PERIOD_END_HOUR === null) return true;
+    const sh = SESSION_PERIOD_START_HOUR;
+    const eh = SESSION_PERIOD_END_HOUR;
+    if (eh > sh) {
+        // Same-day window, e.g. 7–19
+        return hour >= sh && hour < eh;
+    } else {
+        // Crosses midnight, e.g. 19–7
+        return hour >= sh || hour < eh;
+    }
+}
+
 // Load data on page load
 document.addEventListener('DOMContentLoaded', function() {
     loadRndData();
@@ -387,19 +408,21 @@ function renderChart(data, fileType) {
     });
 }
 
-function renderTable(headers, data) {
-    const headerRow = document.getElementById('table-header');
-    const tbody = document.getElementById('table-body');
+function _rowHour(row) {
+    // Parse hour from "Start Time" field (format: "YYYY/MM/DD HH:MM:SS")
+    const t = row['Start Time'];
+    if (!t) return null;
+    const parts = t.split(' ');
+    if (parts.length < 2) return null;
+    return parseInt(parts[1].split(':')[0], 10);
+}
 
-    // Render headers
-    headerRow.innerHTML = '<tr>' + headers.map(h =>
-        `<th class="px-4 py-3 text-left font-medium">${escapeHtml(h)}</th>`
-    ).join('') + '</tr>';
-
-    // Render rows (limit to first 500 for performance)
-    const displayData = data.slice(0, 500);
-    tbody.innerHTML = displayData.map(row =>
-        '<tr class="hover:bg-gray-50 dark:hover:bg-gray-800/50">' +
+function _buildRow(headers, row) {
+    const hour = _rowHour(row);
+    const inWindow = hour === null || _isInPeriodWindow(hour);
+    const dimClass = inWindow ? '' : 'opacity-40';
+    const titleAttr = (!inWindow) ? ' title="Outside period window"' : '';
+    return `<tr class="hover:bg-gray-50 dark:hover:bg-gray-800/50 ${dimClass}"${titleAttr}>` +
         headers.map(h => {
             const val = row[h];
             let displayVal = val;
@@ -410,12 +433,34 @@ function renderTable(headers, data) {
             }
             return `<td class="px-4 py-2 text-gray-700 dark:text-gray-300">${escapeHtml(String(displayVal))}</td>`;
         }).join('') +
-        '</tr>'
-    ).join('');
+        '</tr>';
+}
+
+function renderTable(headers, data) {
+    const headerRow = document.getElementById('table-header');
+    const tbody = document.getElementById('table-body');
+
+    // Render headers — add period window indicator if configured
+    let periodNote = '';
+    if (SESSION_PERIOD_START_HOUR !== null && SESSION_PERIOD_END_HOUR !== null) {
+        function _fmtH(h) { const ampm = h < 12 ? 'AM' : 'PM'; return `${h%12||12}:00 ${ampm}`; }
+        periodNote = ` <span class="ml-2 text-indigo-500 dark:text-indigo-400 font-normal normal-case text-xs" title="Dimmed rows are outside this window">Period: ${_fmtH(SESSION_PERIOD_START_HOUR)} → ${_fmtH(SESSION_PERIOD_END_HOUR)}</span>`;
+    }
+    headerRow.innerHTML = '<tr>' + headers.map((h, i) =>
+        `<th class="px-4 py-3 text-left font-medium">${escapeHtml(h)}${i === 0 ? periodNote : ''}</th>`
+    ).join('') + '</tr>';
+
+    // Render rows (limit to first 500 for performance)
+    const displayData = data.slice(0, 500);
+    tbody.innerHTML = displayData.map(row => _buildRow(headers, row)).join('');
 
     // Update row count
+    const inWindowCount = data.filter(r => { const h = _rowHour(r); return h === null || _isInPeriodWindow(h); }).length;
+    const windowNote = (SESSION_PERIOD_START_HOUR !== null && inWindowCount < data.length)
+        ? ` (${inWindowCount} in period window)`
+        : '';
     document.getElementById('row-count').textContent =
-        data.length > 500 ? `Showing 500 of ${data.length.toLocaleString()} rows` : `${data.length.toLocaleString()} rows`;
+        data.length > 500 ? `Showing 500 of ${data.length.toLocaleString()} rows${windowNote}` : `${data.length.toLocaleString()} rows${windowNote}`;
 
     // Search functionality
     document.getElementById('table-search').addEventListener('input', function(e) {
@@ -427,20 +472,7 @@ function renderTable(headers, data) {
         );
 
         const displayFiltered = filtered.slice(0, 500);
-        tbody.innerHTML = displayFiltered.map(row =>
-            '<tr class="hover:bg-gray-50 dark:hover:bg-gray-800/50">' +
-            headers.map(h => {
-                const val = row[h];
-                let displayVal = val;
-                if (val === null || val === undefined) {
-                    displayVal = '-';
-                } else if (typeof val === 'number') {
-                    displayVal = val.toFixed(1);
-                }
-                return `<td class="px-4 py-2 text-gray-700 dark:text-gray-300">${escapeHtml(String(displayVal))}</td>`;
-            }).join('') +
-            '</tr>'
-        ).join('');
+        tbody.innerHTML = displayFiltered.map(row => _buildRow(headers, row)).join('');
 
         document.getElementById('row-count').textContent =
             filtered.length > 500 ? `Showing 500 of ${filtered.length.toLocaleString()} filtered rows` : `${filtered.length.toLocaleString()} rows`;
diff --git a/templates/session_detail.html b/templates/session_detail.html
new file mode 100644
index 0000000..23d64b4
--- /dev/null
+++ b/templates/session_detail.html
@@ -0,0 +1,437 @@
+{% extends "base.html" %}
+
+{% block title %}{{ session.session_label or 'Session' }} — {{ project.name }}{% endblock %}
+
+{% block content %}
+<div class="max-w-5xl mx-auto">
+    <!-- Breadcrumb -->
+    <nav class="flex items-center space-x-2 text-sm text-gray-500 dark:text-gray-400 mb-4">
+        <a href="/projects" class="hover:text-seismo-orange">Projects</a>
+        <svg class="w-4 h-4" fill="none" stroke="currentColor" viewBox="0 0 24 24">
+            <path stroke-linecap="round" stroke-linejoin="round" stroke-width="2" d="M9 5l7 7-7 7"></path>
+        </svg>
+        <a href="/projects/{{ project_id }}" class="hover:text-seismo-orange">{{ project.name }}</a>
+        <svg class="w-4 h-4" fill="none" stroke="currentColor" viewBox="0 0 24 24">
+            <path stroke-linecap="round" stroke-linejoin="round" stroke-width="2" d="M9 5l7 7-7 7"></path>
+        </svg>
+        <span class="text-gray-900 dark:text-white truncate max-w-xs">{{ session.session_label or ('Session ' + session.id[:8] + '…') }}</span>
+    </nav>
+
+    <!-- Header -->
+    <div class="flex items-start justify-between gap-4 mb-6">
+        <div>
+            <h1 class="text-2xl font-bold text-gray-900 dark:text-white flex items-center gap-3">
+                <svg class="w-7 h-7 text-seismo-orange" fill="none" stroke="currentColor" viewBox="0 0 24 24">
+                    <path stroke-linecap="round" stroke-linejoin="round" stroke-width="2" d="M9 19v-6a2 2 0 00-2-2H5a2 2 0 00-2 2v6a2 2 0 002 2h2a2 2 0 002-2zm0 0V9a2 2 0 012-2h2a2 2 0 012 2v10m-6 0a2 2 0 002 2h2a2 2 0 002-2m0 0V5a2 2 0 012-2h2a2 2 0 012 2v14a2 2 0 01-2 2h-2a2 2 0 01-2-2z"></path>
+                </svg>
+                <span id="header-label">{{ session.session_label or ('Session ' + session.id[:8] + '…') }}</span>
+            </h1>
+            {% if location %}
+            <p class="text-sm text-gray-500 dark:text-gray-400 mt-1">{{ location.name }}{% if unit %} · {{ unit.id }}{% endif %}</p>
+            {% endif %}
+        </div>
+        <div class="flex items-center gap-2 shrink-0">
+            {% if session.status == 'completed' %}
+            <span class="px-3 py-1 text-xs font-medium bg-green-100 text-green-800 dark:bg-green-900/30 dark:text-green-300 rounded-full">Completed</span>
+            {% elif session.status == 'recording' %}
+            <span class="px-3 py-1 text-xs font-medium bg-red-100 text-red-800 dark:bg-red-900/30 dark:text-red-300 rounded-full flex items-center gap-1">
+                <span class="w-2 h-2 bg-red-500 rounded-full animate-pulse"></span> Recording
+            </span>
+            {% endif %}
+        </div>
+    </div>
+
+    <div class="grid grid-cols-1 lg:grid-cols-3 gap-6">
+
+        <!-- LEFT COLUMN: Info + Edit -->
+        <div class="lg:col-span-1 space-y-4">
+
+            <!-- Session Info Card -->
+            <div class="bg-white dark:bg-slate-800 rounded-xl border border-gray-200 dark:border-gray-700 p-5">
+                <h2 class="text-sm font-semibold text-gray-700 dark:text-gray-300 uppercase tracking-wide mb-3">Session Info</h2>
+                <dl class="space-y-2 text-sm">
+                    <div class="flex justify-between">
+                        <dt class="text-gray-500 dark:text-gray-400">Label</dt>
+                        <dd class="font-medium text-gray-900 dark:text-white text-right max-w-[180px] truncate"
+                            id="info-label">{{ session.session_label or '—' }}</dd>
+                    </div>
+                    <div class="flex justify-between">
+                        <dt class="text-gray-500 dark:text-gray-400">Location</dt>
+                        <dd class="font-medium text-gray-900 dark:text-white">{{ location.name if location else '—' }}</dd>
+                    </div>
+                    <div class="flex justify-between">
+                        <dt class="text-gray-500 dark:text-gray-400">Period</dt>
+                        <dd class="font-medium text-gray-900 dark:text-white" id="info-period">
+                            {% set PLABELS = {'weekday_day':'Weekday Day','weekday_night':'Weekday Night','weekend_day':'Weekend Day','weekend_night':'Weekend Night'} %}
+                            {{ PLABELS.get(session.period_type, '—') }}
+                        </dd>
+                    </div>
+                    {% if effective_range %}
+                    <div class="flex justify-between">
+                        <dt class="text-gray-500 dark:text-gray-400">Effective</dt>
+                        <dd class="font-medium text-indigo-600 dark:text-indigo-400 text-right text-xs" id="info-effective">{{ effective_range }}</dd>
+                    </div>
+                    {% else %}
+                    <div class="flex justify-between hidden" id="info-effective-row">
+                        <dt class="text-gray-500 dark:text-gray-400">Effective</dt>
+                        <dd class="font-medium text-indigo-600 dark:text-indigo-400 text-right text-xs" id="info-effective"></dd>
+                    </div>
+                    {% endif %}
+                    <div class="flex justify-between">
+                        <dt class="text-gray-500 dark:text-gray-400">Report Date</dt>
+                        <dd class="font-medium text-gray-900 dark:text-white" id="info-report-date">
+                            {{ report_date or '— (auto)' }}
+                        </dd>
+                    </div>
+                    {% if session.started_at %}
+                    <div class="flex justify-between">
+                        <dt class="text-gray-500 dark:text-gray-400">Started</dt>
+                        <dd class="font-medium text-gray-900 dark:text-white text-right">{{ session.started_at|local_datetime }}</dd>
+                    </div>
+                    {% endif %}
+                    {% if session.stopped_at %}
+                    <div class="flex justify-between">
+                        <dt class="text-gray-500 dark:text-gray-400">Ended</dt>
+                        <dd class="font-medium text-gray-900 dark:text-white text-right">{{ session.stopped_at|local_datetime }}</dd>
+                    </div>
+                    {% endif %}
+                    {% if session.duration_seconds %}
+                    <div class="flex justify-between">
+                        <dt class="text-gray-500 dark:text-gray-400">Duration</dt>
+                        <dd class="font-medium text-gray-900 dark:text-white">{{ session.duration_seconds // 3600 }}h {{ (session.duration_seconds % 3600) // 60 }}m</dd>
+                    </div>
+                    {% endif %}
+                    {% if session.device_model %}
+                    <div class="flex justify-between">
+                        <dt class="text-gray-500 dark:text-gray-400">Device Model</dt>
+                        <dd class="font-medium text-gray-900 dark:text-white">{{ session.device_model }}</dd>
+                    </div>
+                    {% endif %}
+                    {% if session_meta.get('store_name') %}
+                    <div class="flex justify-between">
+                        <dt class="text-gray-500 dark:text-gray-400">Store Name</dt>
+                        <dd class="font-medium text-gray-900 dark:text-white">{{ session_meta.store_name }}</dd>
+                    </div>
+                    {% endif %}
+                    {% if session_meta.get('serial_number') %}
+                    <div class="flex justify-between">
+                        <dt class="text-gray-500 dark:text-gray-400">Serial #</dt>
+                        <dd class="font-medium text-gray-900 dark:text-white">{{ session_meta.serial_number }}</dd>
+                    </div>
+                    {% endif %}
+                </dl>
+            </div>
+
+            <!-- Edit Card -->
+            <div class="bg-white dark:bg-slate-800 rounded-xl border border-gray-200 dark:border-gray-700 p-5">
+                <h2 class="text-sm font-semibold text-gray-700 dark:text-gray-300 uppercase tracking-wide mb-4">Edit Session</h2>
+                <form id="edit-form" onsubmit="saveSession(event)">
+
+                    <!-- Label -->
+                    <div class="mb-4">
+                        <label class="block text-xs text-gray-500 dark:text-gray-400 mb-1">Label</label>
+                        <input type="text" id="edit-label" name="session_label"
+                               value="{{ session.session_label or '' }}"
+                               placeholder="e.g. NRL-1 — Mon 3/24 — Night"
+                               class="w-full text-sm bg-gray-50 dark:bg-slate-700 border border-gray-200 dark:border-gray-600 rounded-lg px-3 py-2 text-gray-900 dark:text-white focus:outline-none focus:border-seismo-orange">
+                    </div>
+
+                    <!-- Section: Required Recording Window -->
+                    <div class="mb-4 p-3 bg-indigo-50 dark:bg-indigo-900/20 rounded-lg border border-indigo-100 dark:border-indigo-800">
+                        <p class="text-xs font-semibold text-indigo-700 dark:text-indigo-300 mb-0.5">Required Recording Window</p>
+                        <p class="text-xs text-indigo-500 dark:text-indigo-400 mb-3">The hours that count for reports. Only data within this window is included.</p>
+
+                        <div class="space-y-2">
+                            <div>
+                                <label class="block text-xs text-gray-500 dark:text-gray-400 mb-1">Period Type</label>
+                                <select id="edit-period-type" name="period_type"
+                                        onchange="fillPeriodDefaults()"
+                                        class="w-full text-sm bg-white dark:bg-slate-700 border border-gray-200 dark:border-gray-600 rounded-lg px-3 py-2 text-gray-900 dark:text-white focus:outline-none focus:border-seismo-orange">
+                                    <option value="">— Not Set —</option>
+                                    <option value="weekday_day"   {% if session.period_type == 'weekday_day' %}selected{% endif %}>Weekday Day</option>
+                                    <option value="weekday_night" {% if session.period_type == 'weekday_night' %}selected{% endif %}>Weekday Night</option>
+                                    <option value="weekend_day"   {% if session.period_type == 'weekend_day' %}selected{% endif %}>Weekend Day</option>
+                                    <option value="weekend_night" {% if session.period_type == 'weekend_night' %}selected{% endif %}>Weekend Night</option>
+                                </select>
+                            </div>
+
+                            <div class="grid grid-cols-2 gap-2">
+                                <div>
+                                    <label class="block text-xs text-gray-500 dark:text-gray-400 mb-1">From (hour)</label>
+                                    <div class="relative">
+                                        <input type="number" min="0" max="23" id="edit-start-hour" name="period_start_hour"
+                                               value="{{ session.period_start_hour if session.period_start_hour is not none else '' }}"
+                                               placeholder="e.g. 19"
+                                               oninput="updateWindowPreview()"
+                                               class="w-full text-sm bg-white dark:bg-slate-700 border border-gray-200 dark:border-gray-600 rounded-lg px-3 py-2 text-gray-900 dark:text-white focus:outline-none focus:border-seismo-orange">
+                                    </div>
+                                </div>
+                                <div>
+                                    <label class="block text-xs text-gray-500 dark:text-gray-400 mb-1">To (hour)</label>
+                                    <input type="number" min="0" max="23" id="edit-end-hour" name="period_end_hour"
+                                           value="{{ session.period_end_hour if session.period_end_hour is not none else '' }}"
+                                           placeholder="e.g. 7"
+                                           oninput="updateWindowPreview()"
+                                           class="w-full text-sm bg-white dark:bg-slate-700 border border-gray-200 dark:border-gray-600 rounded-lg px-3 py-2 text-gray-900 dark:text-white focus:outline-none focus:border-seismo-orange">
+                                </div>
+                            </div>
+
+                            <!-- Live preview -->
+                            <div id="window-preview" class="text-xs font-medium text-indigo-600 dark:text-indigo-300 min-h-[1rem]">
+                                {% if session.period_start_hour is not none and session.period_end_hour is not none %}
+                                    {% set sh = session.period_start_hour %}
+                                    {% set eh = session.period_end_hour %}
+                                    Window: {{ (sh % 12) or 12 }}:00 {{ 'AM' if sh < 12 else 'PM' }} → {{ (eh % 12) or 12 }}:00 {{ 'AM' if eh < 12 else 'PM' }}{% if eh <= sh %} (crosses midnight){% endif %}
+                                {% endif %}
+                            </div>
+
+                            <div class="mt-2">
+                                <label class="block text-xs text-gray-500 dark:text-gray-400 mb-1">
+                                    Target Date <span class="text-gray-400">(optional — day sessions only)</span>
+                                </label>
+                                <input type="date" id="edit-report-date" name="report_date"
+                                       value="{{ report_date or '' }}"
+                                       class="w-full text-sm bg-white dark:bg-slate-700 border border-gray-200 dark:border-gray-600 rounded-lg px-3 py-2 text-gray-900 dark:text-white focus:outline-none focus:border-seismo-orange">
+                                <p class="text-xs text-gray-400 dark:text-gray-500 mt-1">Leave blank to auto-select the last day with data in the window.</p>
+                            </div>
+                        </div>
+                    </div>
+
+                    <!-- Section: Device On/Off Times -->
+                    <div class="mb-4 p-3 bg-gray-50 dark:bg-slate-700/40 rounded-lg border border-gray-200 dark:border-gray-600">
+                        <p class="text-xs font-semibold text-gray-600 dark:text-gray-400 mb-0.5">Device On/Off Times</p>
+                        <p class="text-xs text-gray-400 dark:text-gray-500 mb-3">When the meter was actually running. Usually set automatically from the data file.</p>
+
+                        <div class="space-y-2">
+                            <div>
+                                <label class="block text-xs text-gray-500 dark:text-gray-400 mb-1">Powered on</label>
+                                <input type="datetime-local" id="edit-started-at" name="started_at"
+                                       value="{{ session.started_at|local_datetime_input if session.started_at else '' }}"
+                                       class="w-full text-sm bg-white dark:bg-slate-700 border border-gray-200 dark:border-gray-600 rounded-lg px-3 py-2 text-gray-900 dark:text-white focus:outline-none focus:border-seismo-orange">
+                            </div>
+                            <div>
+                                <label class="block text-xs text-gray-500 dark:text-gray-400 mb-1">Powered off</label>
+                                <input type="datetime-local" id="edit-stopped-at" name="stopped_at"
+                                       value="{{ session.stopped_at|local_datetime_input if session.stopped_at else '' }}"
+                                       class="w-full text-sm bg-white dark:bg-slate-700 border border-gray-200 dark:border-gray-600 rounded-lg px-3 py-2 text-gray-900 dark:text-white focus:outline-none focus:border-seismo-orange">
+                            </div>
+                        </div>
+                    </div>
+
+                    <div class="flex gap-2">
+                        <button type="submit"
+                                class="flex-1 text-sm py-2 bg-seismo-orange text-white rounded-lg hover:bg-orange-600 transition-colors font-medium">
+                            Save Changes
+                        </button>
+                    </div>
+                    <div id="save-status" class="hidden text-xs text-center pt-2"></div>
+                </form>
+            </div>
+        </div>
+
+        <!-- RIGHT COLUMN: Files + Report Actions -->
+        <div class="lg:col-span-2 space-y-5">
+
+            <!-- Files List -->
+            <div class="bg-white dark:bg-slate-800 rounded-xl border border-gray-200 dark:border-gray-700 overflow-hidden">
+                <div class="px-5 py-4 border-b border-gray-200 dark:border-gray-700 flex items-center justify-between">
+                    <h2 class="text-sm font-semibold text-gray-700 dark:text-gray-300 uppercase tracking-wide">
+                        Data Files
+                        <span class="ml-2 text-xs font-normal text-gray-400">({{ files|length }})</span>
+                    </h2>
+                </div>
+                {% if files %}
+                <div class="divide-y divide-gray-100 dark:divide-gray-700">
+                    {% for f in files %}
+                    {% set fname = f.file_path.split('/')[-1] %}
+                    {% set is_rnd = fname.lower().endswith('.rnd') %}
+                    {% set is_leq = '_leq_' in fname.lower() or fname.lower().startswith('au2_') %}
+                    <div class="flex items-center gap-3 px-5 py-3 hover:bg-gray-50 dark:hover:bg-slate-700/50 transition-colors">
+                        <!-- Icon -->
+                        <div class="shrink-0 w-8 h-8 rounded-lg flex items-center justify-center
+                                    {% if is_rnd %}bg-green-100 dark:bg-green-900/30{% else %}bg-gray-100 dark:bg-gray-700{% endif %}">
+                            {% if is_rnd %}
+                            <svg class="w-4 h-4 text-green-600 dark:text-green-400" fill="none" stroke="currentColor" viewBox="0 0 24 24">
+                                <path stroke-linecap="round" stroke-linejoin="round" stroke-width="2" d="M9 19v-6a2 2 0 00-2-2H5a2 2 0 00-2 2v6a2 2 0 002 2h2a2 2 0 002-2zm0 0V9a2 2 0 012-2h2a2 2 0 012 2v10m-6 0a2 2 0 002 2h2a2 2 0 002-2m0 0V5a2 2 0 012-2h2a2 2 0 012 2v14a2 2 0 01-2 2h-2a2 2 0 01-2-2z"></path>
+                            </svg>
+                            {% else %}
+                            <svg class="w-4 h-4 text-gray-400" fill="none" stroke="currentColor" viewBox="0 0 24 24">
+                                <path stroke-linecap="round" stroke-linejoin="round" stroke-width="2" d="M7 21h10a2 2 0 002-2V9.414a1 1 0 00-.293-.707l-5.414-5.414A1 1 0 0012.586 3H7a2 2 0 00-2 2v14a2 2 0 002 2z"></path>
+                            </svg>
+                            {% endif %}
+                        </div>
+
+                        <!-- Name + meta -->
+                        <div class="min-w-0 flex-1">
+                            <div class="text-sm font-medium text-gray-900 dark:text-white truncate">{{ fname }}</div>
+                            <div class="text-xs text-gray-400 flex items-center gap-2 mt-0.5">
+                                <span>{{ f.file_type | upper }}</span>
+                                {% if f.file_size_bytes %}
+                                <span>{{ (f.file_size_bytes / 1024) | round(1) }} KB</span>
+                                {% endif %}
+                                {% if is_leq %}<span class="text-green-600 dark:text-green-400 font-medium">Leq</span>{% endif %}
+                            </div>
+                        </div>
+
+                        <!-- Actions -->
+                        <div class="flex items-center gap-2 shrink-0">
+                            {% if is_rnd %}
+                            <a href="/api/projects/{{ project_id }}/files/{{ f.id }}/view-rnd"
+                               class="px-2 py-1 text-xs bg-green-600 text-white rounded hover:bg-green-700 transition-colors">
+                                View
+                            </a>
+                            {% if is_leq %}
+                            <button onclick="openSingleFileReport('{{ f.id }}', '{{ fname }}')"
+                                    class="px-2 py-1 text-xs bg-emerald-600 text-white rounded hover:bg-emerald-700 transition-colors">
+                                Report
+                            </button>
+                            {% endif %}
+                            {% endif %}
+                            <a href="/api/projects/{{ project_id }}/files/{{ f.id }}/download"
+                               class="px-2 py-1 text-xs border border-gray-200 dark:border-gray-600 text-gray-600 dark:text-gray-400 rounded hover:bg-gray-100 dark:hover:bg-slate-600 transition-colors">
+                                Download
+                            </a>
+                        </div>
+                    </div>
+                    {% endfor %}
+                </div>
+                {% else %}
+                <div class="px-5 py-10 text-center text-gray-400">
+                    <p>No files found for this session.</p>
+                </div>
+                {% endif %}
+            </div>
+
+            <!-- Report Actions -->
+            <div class="bg-white dark:bg-slate-800 rounded-xl border border-gray-200 dark:border-gray-700 p-5">
+                <h2 class="text-sm font-semibold text-gray-700 dark:text-gray-300 uppercase tracking-wide mb-3">Report Actions</h2>
+
+                {% if session.status == 'completed' %}
+                {% set has_rnd = files | selectattr('file_type', 'equalto', 'rnd') | list | length > 0 %}
+                {% if has_rnd %}
+                <div class="p-3 bg-gray-50 dark:bg-slate-700/50 rounded-lg space-y-2">
+                    <p class="text-xs text-gray-600 dark:text-gray-400">
+                        Use the <strong>Combined Report Wizard</strong> to generate an Excel report for this session, or click <strong>View</strong> on a Leq file above to access per-file reporting.
+                        {% if session.period_start_hour is not none %}
+                        <br><span class="text-indigo-600 dark:text-indigo-400">Period window {{ session.period_start_hour }}:00–{{ session.period_end_hour }}:00 will be applied.</span>
+                        {% endif %}
+                    </p>
+                    <a href="/projects/{{ project_id }}?tab=data"
+                       class="inline-flex items-center gap-2 px-4 py-2 bg-emerald-600 text-white text-sm rounded-lg hover:bg-emerald-700 transition-colors font-medium">
+                        <svg class="w-4 h-4" fill="none" stroke="currentColor" viewBox="0 0 24 24">
+                            <path stroke-linecap="round" stroke-linejoin="round" stroke-width="2" d="M9 17v-2m3 2v-4m3 4v-6m2 10H7a2 2 0 01-2-2V5a2 2 0 012-2h5.586a1 1 0 01.707.293l5.414 5.414a1 1 0 01.293.707V19a2 2 0 01-2 2z"></path>
+                        </svg>
+                        Go to Combined Report Wizard
+                    </a>
+                </div>
+                {% else %}
+                <p class="text-sm text-gray-400 dark:text-gray-500">No .rnd files found — upload data to generate a report.</p>
+                {% endif %}
+                {% else %}
+                <p class="text-sm text-gray-400 dark:text-gray-500">Reports are available after the session is completed.</p>
+                {% endif %}
+            </div>
+
+        </div>
+    </div>
+</div>
+
+<script>
+const PROJECT_ID = '{{ project_id }}';
+const SESSION_ID = '{{ session.id }}';
+
+const PERIOD_DEFAULT_HOURS = {
+    weekday_day:   {start: 7,  end: 19},
+    weekday_night: {start: 19, end: 7},
+    weekend_day:   {start: 7,  end: 19},
+    weekend_night: {start: 19, end: 7},
+};
+
+function fillPeriodDefaults() {
+    const pt = document.getElementById('edit-period-type').value;
+    const defaults = PERIOD_DEFAULT_HOURS[pt];
+    if (defaults) {
+        document.getElementById('edit-start-hour').value = defaults.start;
+        document.getElementById('edit-end-hour').value   = defaults.end;
+    }
+    updateWindowPreview();
+}
+
+function updateWindowPreview() {
+    const sh = parseInt(document.getElementById('edit-start-hour').value, 10);
+    const eh = parseInt(document.getElementById('edit-end-hour').value, 10);
+    const el = document.getElementById('window-preview');
+    if (!el) return;
+    if (isNaN(sh) || isNaN(eh)) { el.textContent = ''; return; }
+    function fmt(h) { return `${h % 12 || 12}:00 ${h < 12 ? 'AM' : 'PM'}`; }
+    const crosses = eh <= sh;
+    el.textContent = `Window: ${fmt(sh)} → ${fmt(eh)}${crosses ? ' (crosses midnight)' : ''}`;
+}
+
+// Run once on load to populate preview if values already set
+document.addEventListener('DOMContentLoaded', updateWindowPreview);
+
+async function saveSession(e) {
+    e.preventDefault();
+    const status = document.getElementById('save-status');
+    status.className = 'text-xs text-center pt-1 text-gray-400';
+    status.textContent = 'Saving…';
+    status.classList.remove('hidden');
+
+    const form = document.getElementById('edit-form');
+    const payload = {};
+
+    const label = form.session_label.value.trim();
+    payload.session_label = label || null;
+
+    const pt = form.period_type.value;
+    payload.period_type = pt || null;
+
+    const sh = form.period_start_hour.value;
+    const eh = form.period_end_hour.value;
+    payload.period_start_hour = sh !== '' ? parseInt(sh, 10) : null;
+    payload.period_end_hour   = eh !== '' ? parseInt(eh, 10) : null;
+
+    const rd = form.report_date.value;
+    payload.report_date = rd || null;
+
+    const sa = form.started_at.value;
+    if (sa) payload.started_at = sa;
+
+    const st = form.stopped_at.value;
+    if (st) payload.stopped_at = st;
+    else if (form.stopped_at.value === '') payload.stopped_at = null;
+
+    try {
+        const resp = await fetch(`/api/projects/${PROJECT_ID}/sessions/${SESSION_ID}`, {
+            method: 'PATCH',
+            headers: {'Content-Type': 'application/json'},
+            body: JSON.stringify(payload),
+        });
+        if (!resp.ok) throw new Error(await resp.text());
+        const result = await resp.json();
+
+        // Update displayed label
+        const newLabel = result.session_label || ('Session ' + SESSION_ID.slice(0, 8) + '…');
+        document.getElementById('header-label').textContent = newLabel;
+        document.getElementById('info-label').textContent = result.session_label || '—';
+        document.getElementById('info-period').textContent = {
+            weekday_day: 'Weekday Day', weekday_night: 'Weekday Night',
+            weekend_day: 'Weekend Day', weekend_night: 'Weekend Night'
+        }[result.period_type] || '—';
+        document.getElementById('info-report-date').textContent = result.report_date || '— (auto)';
+
+        status.className = 'text-xs text-center pt-1 text-green-600 dark:text-green-400';
+        status.textContent = 'Saved!';
+        setTimeout(() => status.classList.add('hidden'), 2500);
+    } catch(err) {
+        status.className = 'text-xs text-center pt-1 text-red-500';
+        status.textContent = 'Error: ' + err.message;
+    }
+}
+
+function openSingleFileReport(fileId, filename) {
+    window.location.href = `/api/projects/${PROJECT_ID}/files/${fileId}/view-rnd`;
+}
+</script>
+{% endblock %}
diff --git a/templates/vibration_location_detail.html b/templates/vibration_location_detail.html
index acb41dd..6afc9d8 100644
--- a/templates/vibration_location_detail.html
+++ b/templates/vibration_location_detail.html
@@ -37,7 +37,7 @@
                 {{ location.name }}
             </h1>
             <p class="text-gray-600 dark:text-gray-400 mt-1">
-                Monitoring Location • {{ project.name }}
+                Monitoring Location &bull; {{ project.name }}
             </p>
         </div>
         <div class="flex gap-2">
@@ -116,20 +116,36 @@
                 <h2 class="text-xl font-semibold text-gray-900 dark:text-white mb-4">Unit Assignment</h2>
                 {% if assigned_unit %}
                 <div class="space-y-4">
+                    <!-- Seismograph row -->
                     <div>
-                        <div class="text-sm text-gray-600 dark:text-gray-400">Assigned Unit</div>
+                        <div class="text-sm text-gray-600 dark:text-gray-400">Seismograph</div>
                         <div class="text-lg font-medium text-gray-900 dark:text-white">
                             <a href="/unit/{{ assigned_unit.id }}" class="text-seismo-orange hover:text-seismo-navy">
                                 {{ assigned_unit.id }}
                             </a>
                         </div>
+                        {% if assigned_unit.unit_type %}
+                        <div class="text-xs text-gray-500 dark:text-gray-400 mt-0.5">{{ assigned_unit.unit_type }}</div>
+                        {% endif %}
                     </div>
-                    {% if assigned_unit.device_type %}
+                    <!-- Modem row -->
                     <div>
-                        <div class="text-sm text-gray-600 dark:text-gray-400">Device Type</div>
-                        <div class="text-gray-900 dark:text-white">{{ assigned_unit.device_type|capitalize }}</div>
+                        <div class="text-sm text-gray-600 dark:text-gray-400">Modem</div>
+                        {% if assigned_modem %}
+                        <div class="text-lg font-medium text-gray-900 dark:text-white">
+                            <a href="/unit/{{ assigned_modem.id }}" class="text-seismo-orange hover:text-seismo-navy">
+                                {{ assigned_modem.id }}
+                            </a>
+                        </div>
+                        {% if assigned_modem.hardware_model or assigned_modem.ip_address %}
+                        <div class="text-xs text-gray-500 dark:text-gray-400 mt-0.5">
+                            {{ assigned_modem.hardware_model or '' }}{% if assigned_modem.hardware_model and assigned_modem.ip_address %} &bull; {% endif %}{{ assigned_modem.ip_address or '' }}
+                        </div>
+                        {% endif %}
+                        {% else %}
+                        <div class="text-sm text-gray-400 dark:text-gray-500 italic">No modem paired</div>
+                        {% endif %}
                     </div>
-                    {% endif %}
                     {% if assignment %}
                     <div>
                         <div class="text-sm text-gray-600 dark:text-gray-400">Assigned Since</div>
@@ -142,10 +158,14 @@
                     </div>
                     {% endif %}
                     {% endif %}
-                    <div class="pt-2">
+                    <div class="pt-2 flex gap-2 flex-wrap">
+                        <button onclick="openSwapModal()"
+                                class="px-4 py-2 bg-seismo-orange text-white rounded-lg hover:bg-seismo-navy transition-colors text-sm">
+                            Swap Unit / Modem
+                        </button>
                         <button onclick="unassignUnit('{{ assignment.id }}')"
-                                class="px-4 py-2 bg-amber-100 text-amber-800 dark:bg-amber-900/30 dark:text-amber-300 rounded-lg hover:bg-amber-200 dark:hover:bg-amber-900/50 transition-colors">
-                            Unassign Unit
+                                class="px-4 py-2 bg-amber-100 text-amber-800 dark:bg-amber-900/30 dark:text-amber-300 rounded-lg hover:bg-amber-200 dark:hover:bg-amber-900/50 transition-colors text-sm">
+                            Unassign
                         </button>
                     </div>
                 </div>
@@ -155,7 +175,7 @@
                         <path stroke-linecap="round" stroke-linejoin="round" stroke-width="2" d="M20 13V6a2 2 0 00-2-2H6a2 2 0 00-2 2v7m16 0v5a2 2 0 01-2 2H6a2 2 0 01-2-2v-5m16 0h-2.586a1 1 0 00-.707.293l-2.414 2.414a1 1 0 01-.707.293h-3.172a1 1 0 01-.707-.293l-2.414-2.414A1 1 0 006.586 13H4"></path>
                     </svg>
                     <p class="text-gray-500 dark:text-gray-400 mb-4">No unit currently assigned</p>
-                    <button onclick="openAssignModal()"
+                    <button onclick="openSwapModal()"
                             class="px-4 py-2 bg-seismo-orange text-white rounded-lg hover:bg-seismo-navy transition-colors">
                         Assign a Unit
                     </button>
@@ -214,47 +234,55 @@
     </div>
 </div>
 
-<!-- Assign Unit Modal -->
-<div id="assign-modal" class="hidden fixed inset-0 bg-black bg-opacity-50 z-50 flex items-center justify-center">
+<!-- Assign / Swap Modal -->
+<div id="swap-modal" class="hidden fixed inset-0 bg-black bg-opacity-50 z-50 flex items-center justify-center">
     <div class="bg-white dark:bg-slate-800 rounded-xl shadow-2xl w-full max-w-2xl max-h-[90vh] overflow-y-auto m-4">
         <div class="p-6 border-b border-gray-200 dark:border-gray-700 flex items-center justify-between">
             <div>
-                <h2 class="text-2xl font-bold text-gray-900 dark:text-white">Assign Unit</h2>
-                <p class="text-gray-600 dark:text-gray-400 mt-1">Attach a seismograph to this location</p>
+                <h2 id="swap-modal-title" class="text-2xl font-bold text-gray-900 dark:text-white">Assign Unit</h2>
+                <p class="text-gray-600 dark:text-gray-400 mt-1">Select a seismograph and optionally a modem for this location</p>
             </div>
-            <button onclick="closeAssignModal()" class="text-gray-500 hover:text-gray-700 dark:text-gray-400 dark:hover:text-gray-200">
+            <button onclick="closeSwapModal()" class="text-gray-500 hover:text-gray-700 dark:text-gray-400 dark:hover:text-gray-200">
                 <svg class="w-6 h-6" fill="none" stroke="currentColor" viewBox="0 0 24 24">
                     <path stroke-linecap="round" stroke-linejoin="round" stroke-width="2" d="M6 18L18 6M6 6l12 12"></path>
                 </svg>
             </button>
         </div>
 
-        <form id="assign-form" class="p-6 space-y-4">
+        <form id="swap-form" class="p-6 space-y-4">
             <div>
-                <label class="block text-sm font-medium text-gray-700 dark:text-gray-300 mb-2">Available Units</label>
-                <select id="assign-unit-id" name="unit_id"
+                <label class="block text-sm font-medium text-gray-700 dark:text-gray-300 mb-2">Seismograph <span class="text-red-500">*</span></label>
+                <select id="swap-unit-id" name="unit_id"
                         class="w-full px-4 py-2 border border-gray-300 dark:border-gray-600 rounded-lg bg-white dark:bg-gray-700 text-gray-900 dark:text-white" required>
                     <option value="">Loading units...</option>
                 </select>
-                <p id="assign-empty" class="hidden text-xs text-gray-500 mt-2">No available seismographs for this project.</p>
+                <p id="swap-units-empty" class="hidden text-xs text-gray-500 mt-1">No available seismographs.</p>
+            </div>
+
+            <div>
+                <label class="block text-sm font-medium text-gray-700 dark:text-gray-300 mb-2">Modem <span class="text-xs text-gray-400">(optional)</span></label>
+                <select id="swap-modem-id" name="modem_id"
+                        class="w-full px-4 py-2 border border-gray-300 dark:border-gray-600 rounded-lg bg-white dark:bg-gray-700 text-gray-900 dark:text-white">
+                    <option value="">No modem</option>
+                </select>
             </div>
 
             <div>
                 <label class="block text-sm font-medium text-gray-700 dark:text-gray-300 mb-2">Notes</label>
-                <textarea id="assign-notes" name="notes" rows="2"
+                <textarea id="swap-notes" name="notes" rows="2"
                           class="w-full px-4 py-2 border border-gray-300 dark:border-gray-600 rounded-lg bg-white dark:bg-gray-700 text-gray-900 dark:text-white"></textarea>
             </div>
 
-            <div id="assign-error" class="hidden text-sm text-red-600"></div>
+            <div id="swap-error" class="hidden text-sm text-red-600"></div>
 
             <div class="flex justify-end gap-3 pt-2">
-                <button type="button" onclick="closeAssignModal()"
+                <button type="button" onclick="closeSwapModal()"
                         class="px-6 py-2 border border-gray-300 dark:border-gray-600 rounded-lg text-gray-700 dark:text-gray-300 hover:bg-gray-50 dark:hover:bg-gray-700">
                     Cancel
                 </button>
-                <button type="submit"
+                <button type="submit" id="swap-submit-btn"
                         class="px-6 py-2 bg-seismo-orange hover:bg-seismo-navy text-white rounded-lg font-medium">
-                    Assign Unit
+                    Assign
                 </button>
             </div>
         </form>
@@ -264,6 +292,7 @@
 <script>
 const projectId = "{{ project_id }}";
 const locationId = "{{ location_id }}";
+const hasAssignment = {{ 'true' if assigned_unit else 'false' }};
 
 // Tab switching
 function switchTab(tabName) {
@@ -314,60 +343,89 @@ document.getElementById('location-settings-form').addEventListener('submit', asy
     }
 });
 
-// Assign modal
-function openAssignModal() {
-    document.getElementById('assign-modal').classList.remove('hidden');
-    loadAvailableUnits();
+// Swap / Assign modal
+async function openSwapModal() {
+    document.getElementById('swap-modal').classList.remove('hidden');
+    document.getElementById('swap-modal-title').textContent = hasAssignment ? 'Swap Unit / Modem' : 'Assign Unit';
+    document.getElementById('swap-submit-btn').textContent = hasAssignment ? 'Swap' : 'Assign';
+    document.getElementById('swap-error').classList.add('hidden');
+    document.getElementById('swap-notes').value = '';
+    await Promise.all([loadSwapUnits(), loadSwapModems()]);
 }
 
-function closeAssignModal() {
-    document.getElementById('assign-modal').classList.add('hidden');
+function closeSwapModal() {
+    document.getElementById('swap-modal').classList.add('hidden');
 }
 
-async function loadAvailableUnits() {
+async function loadSwapUnits() {
     try {
         const response = await fetch(`/api/projects/${projectId}/available-units?location_type=vibration`);
-        if (!response.ok) throw new Error('Failed to load available units');
+        if (!response.ok) throw new Error('Failed to load units');
         const data = await response.json();
-        const select = document.getElementById('assign-unit-id');
-        select.innerHTML = '<option value="">Select a unit</option>';
+        const select = document.getElementById('swap-unit-id');
+        select.innerHTML = '<option value="">Select a seismograph</option>';
 
         if (!data.length) {
-            document.getElementById('assign-empty').classList.remove('hidden');
-            return;
+            document.getElementById('swap-units-empty').classList.remove('hidden');
+        } else {
+            document.getElementById('swap-units-empty').classList.add('hidden');
         }
 
         data.forEach(unit => {
             const option = document.createElement('option');
             option.value = unit.id;
-            option.textContent = `${unit.id} • ${unit.model || unit.device_type}`;
+            option.textContent = unit.id + (unit.model ? ` \u2022 ${unit.model}` : '') + (unit.location ? ` \u2014 ${unit.location}` : '');
             select.appendChild(option);
         });
     } catch (err) {
-        const errorEl = document.getElementById('assign-error');
-        errorEl.textContent = err.message || 'Failed to load units.';
-        errorEl.classList.remove('hidden');
+        document.getElementById('swap-error').textContent = 'Failed to load seismographs.';
+        document.getElementById('swap-error').classList.remove('hidden');
     }
 }
 
-document.getElementById('assign-form').addEventListener('submit', async function(e) {
+async function loadSwapModems() {
+    try {
+        const response = await fetch(`/api/projects/${projectId}/available-modems`);
+        if (!response.ok) throw new Error('Failed to load modems');
+        const data = await response.json();
+        const select = document.getElementById('swap-modem-id');
+        select.innerHTML = '<option value="">No modem</option>';
+
+        data.forEach(modem => {
+            const option = document.createElement('option');
+            option.value = modem.id;
+            let label = modem.id;
+            if (modem.hardware_model) label += ` \u2022 ${modem.hardware_model}`;
+            if (modem.ip_address) label += ` \u2014 ${modem.ip_address}`;
+            option.textContent = label;
+            select.appendChild(option);
+        });
+    } catch (err) {
+        // Modem list failure is non-fatal — just leave blank
+        console.warn('Failed to load modems:', err);
+    }
+}
+
+document.getElementById('swap-form').addEventListener('submit', async function(e) {
     e.preventDefault();
 
-    const unitId = document.getElementById('assign-unit-id').value;
-    const notes = document.getElementById('assign-notes').value.trim();
+    const unitId = document.getElementById('swap-unit-id').value;
+    const modemId = document.getElementById('swap-modem-id').value;
+    const notes = document.getElementById('swap-notes').value.trim();
 
     if (!unitId) {
-        document.getElementById('assign-error').textContent = 'Select a unit to assign.';
-        document.getElementById('assign-error').classList.remove('hidden');
+        document.getElementById('swap-error').textContent = 'Please select a seismograph.';
+        document.getElementById('swap-error').classList.remove('hidden');
         return;
     }
 
     try {
         const formData = new FormData();
         formData.append('unit_id', unitId);
-        formData.append('notes', notes);
+        if (modemId) formData.append('modem_id', modemId);
+        if (notes) formData.append('notes', notes);
 
-        const response = await fetch(`/api/projects/${projectId}/locations/${locationId}/assign`, {
+        const response = await fetch(`/api/projects/${projectId}/locations/${locationId}/swap`, {
             method: 'POST',
             body: formData
         });
@@ -379,9 +437,8 @@ document.getElementById('assign-form').addEventListener('submit', async function
 
         window.location.reload();
     } catch (err) {
-        const errorEl = document.getElementById('assign-error');
-        errorEl.textContent = err.message || 'Failed to assign unit.';
-        errorEl.classList.remove('hidden');
+        document.getElementById('swap-error').textContent = err.message || 'Failed to assign unit.';
+        document.getElementById('swap-error').classList.remove('hidden');
     }
 });
 
@@ -405,11 +462,11 @@ async function unassignUnit(assignmentId) {
 }
 
 document.addEventListener('keydown', function(e) {
-    if (e.key === 'Escape') closeAssignModal();
+    if (e.key === 'Escape') closeSwapModal();
 });
 
-document.getElementById('assign-modal')?.addEventListener('click', function(e) {
-    if (e.target === this) closeAssignModal();
+document.getElementById('swap-modal')?.addEventListener('click', function(e) {
+    if (e.target === this) closeSwapModal();
 });
 </script>
 {% endblock %}