diff --git a/net_alerter/net_alerter.py b/net_alerter/net_alerter.py
index e594f84..c41a4b5 100644
--- a/net_alerter/net_alerter.py
+++ b/net_alerter/net_alerter.py
@@ -953,9 +953,6 @@ def update_occupancy_state() -> None:
 
 def on_arrival(mac: str, ip: str, hostname: str = "") -> None:
     """Handle device arrival."""
-    # Update passive observation tracking
-    _update_last_seen(mac)
-    
     # Infrastructure IPs never trigger alerts
     if ip in infrastructure_ips:
         logging.debug(f"Ignoring infrastructure IP {ip} (MAC:{mac})")
@@ -1758,10 +1755,10 @@ def personal_watchdog() -> None:
             time.sleep(60)  # Check every minute
             now = time.time()
             
-            # Get current set of personal devices without holding lock for long
-            with personal_lock:
-                tracked = set(personal_devices)
-            
+            # Track all personal devices currently in known_devices (not just enrolled set)
+            with known_lock:
+                tracked = {mac for mac in known_devices if is_personal_device(mac)}
+
             for mac in tracked:
                 # Get last_seen timestamp
                 with last_seen_lock: