diff --git a/server.py b/server.py
index b36aa1c..9745ea9 100644
--- a/server.py
+++ b/server.py
@@ -33,6 +33,9 @@ PREDICTION_HISTORY = []
 PREDICTION_HISTORY_MAX_LENGTH = 3
 PREVIOUS_STATE = "unknown"
 LAST_OPEN_SAVE_TIME = None
+DOOR_OPEN_START_TIME = None
+OPEN_ALERT_THRESHOLDS_MINUTES = [5, 15, 30, 60, 120]
+OPEN_ALERTS_SENT_FOR_CURRENT_OPENING = []
 
 
 def get_derived_state():
@@ -165,16 +168,32 @@ async def monitor_garage_door(app):
 
 async def monitor_state_transitions(app):
     """Periodically checks for state transitions and logs them."""
-    global PREVIOUS_STATE
+    global PREVIOUS_STATE, DOOR_OPEN_START_TIME, OPEN_ALERTS_SENT_FOR_CURRENT_OPENING
     logging.info("Starting state transition monitoring task.")
     while True:
         try:
             await asyncio.sleep(5)
             current_state = get_derived_state()
-            if current_state != "unknown":
-                if current_state != PREVIOUS_STATE:
-                    logging.info(f"State transitioned from '{PREVIOUS_STATE}' to '{current_state}'.")
+            if current_state != "unknown" and current_state != PREVIOUS_STATE:
+                logging.info(f"State transitioned from '{PREVIOUS_STATE}' to '{current_state}'.")
                 PREVIOUS_STATE = current_state
+
+            if current_state == 'open':
+                if DOOR_OPEN_START_TIME is None:
+                    DOOR_OPEN_START_TIME = datetime.now()
+                    OPEN_ALERTS_SENT_FOR_CURRENT_OPENING = []
+                
+                open_duration = datetime.now() - DOOR_OPEN_START_TIME
+                open_duration_minutes = open_duration.total_seconds() / 60
+
+                for threshold in OPEN_ALERT_THRESHOLDS_MINUTES:
+                    if open_duration_minutes >= threshold and threshold not in OPEN_ALERTS_SENT_FOR_CURRENT_OPENING:
+                        logging.info(f"ALERT: Garage door has been open for {threshold} minutes.")
+                        OPEN_ALERTS_SENT_FOR_CURRENT_OPENING.append(threshold)
+            else:
+                DOOR_OPEN_START_TIME = None
+                OPEN_ALERTS_SENT_FOR_CURRENT_OPENING = []
+
         except asyncio.CancelledError:
             logging.info("State transition monitoring task cancelled.")
             break