rain triggering the alarm

As the title says, the alarm in my late model 111R triggered several times last night when the car was parked up in heavy rain. Far too much rain for the scrotes to be out trying to nick cars so the likely culprit is the weather itself. The alarm is the standard Lotus one.

The most likely cause is water in the system somewhere but where? For that matter, where is the control box for the alarm itself?

Any ideas?

Got to admit that I didnt count the flashes - it was absolutely pi88ing it down at the time. And since the car never normally goes out in the rain, it could be a long time before the problem recurrs. But thanks anyway.