If by alarm unit you mean the siren module, then you can unplug that. ( located center of cowl under the plastic cover )
If you mean the central security and locking pump, then you may be right, it could have gotten wet.
It is under the trunk (boot) floorboard, you have to remove a bunch of trim to get to it.
Just locate the yellow air tubes - they will lead you to it.

Did you check the 3 BIG fuses in the little box in front of the battery ?