PT Cruiser Car Alarm

[RickHill]

I have a 2001 PT Cruiser. When we lock the doors the car alarm will go off some time later, for no apparent reason. Sometimes it is 10 minutes, sometimes it is several hours. We thought perhaps the heat buildup inside the car on a sunny day was doing something, but it goes off at night, in the rain, and seems to be fairly random. Any suggestions?