Only saying across the battery to determind if was the alarm to start with, because if it was taking a large drain only when the alarm was switched on, then it may signal the alarm is at fault, but if it drains when alarm is on and off, then start ruling out things like the boot light after.
Also meant to mention when I found my problem to be the diode on the alternator, it was draining the battery roughly 0.01v per second, and can be checked easily enough by removing the cable to it and the drainage stopped.