I had exactly the same problem, my alarm would go off for exactly thirty seconds on starting the car, after an audio "install" my battery was shagged, after about a week of not driving the car the battery was dead and would not recover, even with a solid charge, the car was even spluttering under load. I got a deepcycle batt and all problems dissappeared, my alarm however is installed somewhere and I cant find it at all, when I disconnected the battery the alarm went off for five cycles of 30 secs so be prepared just in case.