diff --git a/backend/migrate_add_mic_unit_pref.py b/backend/migrate_add_mic_unit_pref.py
new file mode 100644
index 0000000..b471949
--- /dev/null
+++ b/backend/migrate_add_mic_unit_pref.py
@@ -0,0 +1,56 @@
+#!/usr/bin/env python3
+"""
+Database migration: Add mic_unit_pref column to user_preferences.
+
+Adds a single field controlling the mic channel's unit on the event-
+report waveform chart in the SFM event detail modal.  "dBL" (default)
+or "psi".  Peaks and KPI tiles elsewhere are always dBL regardless.
+
+Idempotent — safe to re-run.
+"""
+
+import sqlite3
+from pathlib import Path
+
+
+def migrate():
+    possible_paths = [
+        Path("data/seismo_fleet.db"),
+        Path("data/sfm.db"),
+        Path("data/seismo.db"),
+    ]
+    db_path = next((p for p in possible_paths if p.exists()), None)
+    if db_path is None:
+        print(f"Database not found in any of: {[str(p) for p in possible_paths]}")
+        print("Will be created with the new column when models.py initialises.")
+        return
+
+    print(f"Using database: {db_path}")
+    conn = sqlite3.connect(db_path)
+    cur = conn.cursor()
+
+    cur.execute("PRAGMA table_info(user_preferences)")
+    existing = {row[1] for row in cur.fetchall()}
+
+    if "mic_unit_pref" in existing:
+        print("mic_unit_pref already exists — nothing to do.")
+        conn.close()
+        return
+
+    cur.execute(
+        "ALTER TABLE user_preferences "
+        "ADD COLUMN mic_unit_pref TEXT DEFAULT 'dBL'"
+    )
+    # Backfill the single row that should exist (id=1) to the default,
+    # in case the column ends up NULL on existing rows.
+    cur.execute(
+        "UPDATE user_preferences SET mic_unit_pref = 'dBL' "
+        "WHERE mic_unit_pref IS NULL"
+    )
+    conn.commit()
+    conn.close()
+    print("Added mic_unit_pref to user_preferences (default 'dBL').")
+
+
+if __name__ == "__main__":
+    migrate()
diff --git a/backend/models.py b/backend/models.py
index 3ba1e11..5be50ea 100644
--- a/backend/models.py
+++ b/backend/models.py
@@ -135,6 +135,9 @@ class UserPreferences(Base):
     calibration_warning_days = Column(Integer, default=30)
     status_ok_threshold_hours = Column(Integer, default=12)
     status_pending_threshold_hours = Column(Integer, default=24)
+    # Mic display units on the event-report waveform chart only — peaks
+    # and KPI tiles elsewhere are always dBL.  "dBL" (default) or "psi".
+    mic_unit_pref = Column(String, default="dBL")
     updated_at = Column(DateTime, default=datetime.utcnow, onupdate=datetime.utcnow)
 
 
diff --git a/backend/routers/settings.py b/backend/routers/settings.py
index e32f4d6..3b01e70 100644
--- a/backend/routers/settings.py
+++ b/backend/routers/settings.py
@@ -267,6 +267,7 @@ class PreferencesUpdate(BaseModel):
     calibration_warning_days: Optional[int] = None
     status_ok_threshold_hours: Optional[int] = None
     status_pending_threshold_hours: Optional[int] = None
+    mic_unit_pref: Optional[str] = None
 
 
 @router.get("/preferences")
@@ -293,6 +294,7 @@ def get_preferences(db: Session = Depends(get_db)):
         "calibration_warning_days": prefs.calibration_warning_days,
         "status_ok_threshold_hours": prefs.status_ok_threshold_hours,
         "status_pending_threshold_hours": prefs.status_pending_threshold_hours,
+        "mic_unit_pref": prefs.mic_unit_pref or "dBL",
         "updated_at": prefs.updated_at.isoformat() if prefs.updated_at else None
     }
 
@@ -334,6 +336,7 @@ def update_preferences(
         "calibration_warning_days": prefs.calibration_warning_days,
         "status_ok_threshold_hours": prefs.status_ok_threshold_hours,
         "status_pending_threshold_hours": prefs.status_pending_threshold_hours,
+        "mic_unit_pref": prefs.mic_unit_pref or "dBL",
         "updated_at": prefs.updated_at.isoformat() if prefs.updated_at else None
     }
 
diff --git a/templates/settings.html b/templates/settings.html
index ba5532e..662a70e 100644
--- a/templates/settings.html
+++ b/templates/settings.html
@@ -122,6 +122,21 @@
                         How often the dashboard should refresh automatically
                     </p>
                 </div>
+
+                <!-- Event-Report Mic Units -->
+                <div>
+                    <label for="mic-unit-pref" class="block text-sm font-medium text-gray-700 dark:text-gray-300 mb-2">
+                        Event Report — Mic Channel Units
+                    </label>
+                    <select id="mic-unit-pref"
+                            class="w-full max-w-md px-4 py-2 text-gray-900 dark:text-gray-100 bg-gray-50 dark:bg-gray-700 border border-gray-300 dark:border-gray-600 rounded-lg focus:outline-none focus:ring-2 focus:ring-seismo-orange">
+                        <option value="dBL" selected>dB(L) — sound pressure level</option>
+                        <option value="psi">psi — raw pressure</option>
+                    </select>
+                    <p class="text-xs text-gray-500 dark:text-gray-400 mt-1">
+                        Applies only to the waveform chart inside the event detail modal.  Peak values everywhere else (tables, KPIs, modal summary) stay in dB(L) regardless.
+                    </p>
+                </div>
             </div>
 
             <button onclick="saveGeneralSettings()" class="mt-6 px-6 py-3 bg-seismo-orange hover:bg-orange-600 text-white rounded-lg transition-colors">
@@ -771,6 +786,9 @@ async function loadPreferences() {
         // Load auto-refresh interval
         document.getElementById('refresh-interval').value = prefs.auto_refresh_interval || 10;
 
+        // Load event-report mic units
+        document.getElementById('mic-unit-pref').value = prefs.mic_unit_pref || 'dBL';
+
         // Load status thresholds
         document.getElementById('ok-threshold').value = prefs.status_ok_threshold_hours || 12;
         document.getElementById('pending-threshold').value = prefs.status_pending_threshold_hours || 24;
@@ -788,6 +806,7 @@ async function saveGeneralSettings() {
     const timezone = document.getElementById('timezone-select').value;
     const theme = document.querySelector('input[name="theme"]:checked').value;
     const autoRefreshInterval = parseInt(document.getElementById('refresh-interval').value);
+    const micUnitPref = document.getElementById('mic-unit-pref').value;
 
     try {
         const response = await fetch('/api/settings/preferences', {
@@ -796,7 +815,8 @@ async function saveGeneralSettings() {
             body: JSON.stringify({
                 timezone,
                 theme,
-                auto_refresh_interval: autoRefreshInterval
+                auto_refresh_interval: autoRefreshInterval,
+                mic_unit_pref: micUnitPref
             })
         });