We use these kind of water alarms everywhere, and they really work. I've even taped them into my Calfo so the alarm goes off if there's a drainage problem.

Woot (Home) has Leak Frogs for cheap today:

2 for $10 plus $5 shipping

4 for $20 plus $5 shipping

6 for $30 plus $5 shipping

Tax too, since they are in Texas (now part of Amazon).

http://home.woot.com/offers/leakfrog...larm-2-pack-13

Obviously I have no financial interest in this company (I wish...).