Dr.Q

I just bought a 1998 Formula Monday, LS1 w/6-speed. I let it sit monday night in my driveway and the battery was dead when I tried to start it Tuesday afternoon. I'm guessing that maybe the alarm's putting a large draw on the battery? But what else is common on a stock car so far as electrical problems causing the battery to die? It has a brand new battery and the connections are clean...thinking it might have something to do with a mod the previous owner did. But is there just a switch on the alarm computer to shut it off or do I have to pull a connector? Also annoying because I don't have the remote, just keys

At least I got the car at a great deal.