Quickly and easily hack a smoke detector into a basement, sump pump water sensor,
1.) New/Used smoke detector with a test button
2.) Soldering kit
4.) Wire cutters / strippers
4.) Duct Seal (or other non-conductive adhesive
Step 1: Add Your Wires
Remove the cover to the smoke detector, you should be able to find where and how the test button works. Next take 2 pieces of wire any length and solder them to each contact point of the test switch.
*TIP* (once soldered touch and hold the other ends of the wire together for a few seconds to verify that it works)
Step 2: Finish
I used Duct seal to hold the wires together, it's tacky, waterproof, and non-conductive.
Encase the wires in a gob of duct seal and place wherever you want the alarm to go off when water is present.
Retest again by splashing some water over both contact points to confirm operation.
You're all set!