diff --git a/sfm/database.py b/sfm/database.py
index 8c492f5..156d31d 100644
--- a/sfm/database.py
+++ b/sfm/database.py
@@ -564,21 +564,79 @@ class SeismoDb:
 
     def query_units(self) -> list[dict]:
         """
-        Return one row per known serial with summary stats:
-        last_seen, total_events, total_monitor_entries.
+        Return one row per known serial with summary stats.
+
+        Aggregates from BOTH source tables:
+          - `events`        — populated by every ingest path
+                              (live ACH, /db/import/blastware_file
+                              from the series3-watcher forwarder, etc.)
+          - `ach_sessions`  — only populated by the live ACH server;
+                              empty for events that came in via the
+                              BW-importer route.
+
+        Earlier this method only joined on `ach_sessions`, which made
+        watcher-forwarded units invisible to the SFM webapp's fleet
+        overview even though their events were correctly populated in
+        `events`.  Now we union the two and surface every serial that
+        has activity in either table.
+
+        Fields:
+          serial                — unit serial number (e.g. "BE11529")
+          last_seen             — most recent of MAX(events.timestamp)
+                                  and MAX(ach_sessions.session_time)
+          total_events          — COUNT(*) from `events` (the
+                                  authoritative count regardless of
+                                  ingest path)
+          total_monitor_entries — from `ach_sessions`, 0 when absent
+          total_sessions        — COUNT(*) from `ach_sessions`, 0 when absent
         """
         with self._connect() as conn:
-            rows = conn.execute(
-                """
-                SELECT
-                    s.serial,
-                    MAX(s.session_time)  AS last_seen,
-                    SUM(s.events_downloaded)  AS total_events,
-                    SUM(s.monitor_entries)    AS total_monitor_entries,
-                    COUNT(*)                  AS total_sessions
-                FROM ach_sessions s
-                GROUP BY s.serial
-                ORDER BY last_seen DESC
-                """
-            ).fetchall()
-        return [dict(r) for r in rows]
+            event_stats = {
+                row["serial"]: row
+                for row in conn.execute(
+                    """
+                    SELECT serial,
+                           MAX(timestamp) AS last_event_at,
+                           COUNT(*)        AS total_events
+                      FROM events
+                     GROUP BY serial
+                    """,
+                ).fetchall()
+            }
+            session_stats = {
+                row["serial"]: row
+                for row in conn.execute(
+                    """
+                    SELECT serial,
+                           MAX(session_time)         AS last_session_at,
+                           SUM(monitor_entries)      AS total_monitor_entries,
+                           COUNT(*)                  AS total_sessions
+                      FROM ach_sessions
+                     GROUP BY serial
+                    """,
+                ).fetchall()
+            }
+
+        all_serials = set(event_stats) | set(session_stats)
+        units = []
+        for serial in all_serials:
+            e = event_stats.get(serial)
+            s = session_stats.get(serial)
+            last_event_at   = e["last_event_at"]   if e else None
+            last_session_at = s["last_session_at"] if s else None
+            # Prefer whichever timestamp is more recent
+            last_seen = max(
+                (t for t in (last_event_at, last_session_at) if t),
+                default=None,
+            )
+            units.append({
+                "serial":                serial,
+                "last_seen":             last_seen,
+                "total_events":          e["total_events"]          if e else 0,
+                "total_monitor_entries": s["total_monitor_entries"] if s else 0,
+                "total_sessions":        s["total_sessions"]        if s else 0,
+            })
+
+        # Sort by last_seen desc; serials with no timestamp at all sink to the bottom.
+        units.sort(key=lambda u: u.get("last_seen") or "", reverse=True)
+        return units