Alarm just starts honking at all hours of the day and night, with no forewarning, no provocation. I ended up pulling the fuses for the horn and the door-locking system to avoid it, for one year driving the car with no trunk access and no horn. Car could only be opened manually on the driver's side when locked. I was in the shop with it twice, and the first time they found nothing. Changed a couple of things, like a switch inside the driver's side door lock, to no avail. Eventually I left the car with the Ford dealership for ten days so they could try different things. In the end it was a water leak that was causing a short in the wiring. They cleaned up the corrosion caused by the wire, sealed up the leak, and it has not been a problem since (about a year now).