After installing a head unit on my car, my alarm would go off randomly. I tried to fix it, but I got fed up with it and just disabled the alarm. All you have to do is get into the fuse box on the pasenger side of the engine, there should be two fuses for the alarm. Yank em out. Thats it. I keep them just incase I decide to fix it someday. Your keyless entry will still work BTW.
Lyn