This has happened 3 times recently. It's always been after I've been sitting in my car for about 20 minutes after unlocking it. Key is in ignition, in "off" position, using valet key. Alarm sounds suddenly. Can't turn it off by starting engine. Only turns off by unlocking door from outside with key. My remote is broken. Anybody knows what causes this? I was told that is is possibly a way to notify driver that valet key is in ignition?