Nice writeup below on how to convert a cheap smoke detector into a water (in your basement) detector. Basically all you are doing is taking the “test” button and extending wires down from it into a sponge, if the sponge gets wet, the circuit completes and the alarm goes off. Could be a good use if you are updating smoke detectors
http://wolfebaine.blogspot.com/2011/12/15-easy-water-detector.html