the alarm going off by itself is being triggered by one of the following inputs and causing the module to think the vehicle is being broken into. If your vehicle is equipped with keyless entry keypad on the door it may be that the keypad has failed and is shorting,causing one of the number buttons to short,letting the module think someone is trying to enter with the wrong code. This can be verified by the keypad lighting up when the alarm goes off. The other thing it may be is that one of the door ajar switches has failed,which is the most likely concern as i have adressed several concerns due to this. The ajar switch fails and causes the module to see a door ajar while the system is armedmwhich makes the module think the vehicle has been broken into and sounds the alarm. This can be verified if the 'door ajar' light comes on intermitently. The best way to diagnose this concern is by using the Ford scantool ( trip to the shop will be nessecary to perform this test and will likely cost $50) and monitoring the 'alarm event' PID, which will identify What has caused the alarm to go off. is will identify the exact cause of the alarm to be triggered.