Any type of short circuit in the alarm system could cause a battery drain. Unfortunately that kind of problem is a real pain to trace because all the wiring is built into the car's harnesses (I'm assuming we're talking about a factory alarm system here), and you were told that it could sometimes cause it. Intermittent electrical problems can be a real bear to track down (I'm an electrical engineer and do it for a living - believe me, it's a pain sometimes lol). Have you had this happen to you since you got the car, or is it just info passed along and you haven't yet seen it happen? If it hasn't happened to you yet, it's going to be almost impossible to track down. You could go to
www.alldata.com and buy a year's subscription to the info on that particular car and use their troubleshooting flowcharts and information to try and trace the problem though - they've probably got resistance and voltage readings for the majority of the sensors on the car, and you may find one that's out of whack by taking some measurements and comparing them to the listed, expected values.