I wanted a water sensor for my water heater that would both alert me in the house, and as remotely when the sensor was tripped.
This is what it looks like:
I analysed how the DS10A worked, and due to sheer luck in its design, the wires going to the magnetic sensor turn out to be ground and signal, and the water sensor conducted enough current between them to allow triggering of the DS10A:
Wiring is totally trivial, you only need to use a 3rd wire connected to the plus from the 2 batteries, and it "just works". For extra credit, I wired a buzzer between signal and ground, and my water sensor passed enough current to allow the buzzer to run.
I used the Phantom YoYo High Sensitivity Water Sensor which was $10, but apparently you can get one that should work too from seedstudio for $3
The DS10A, I have a stack of, which you can sometimes find on ebay for cheap in bundles, and my house is already wired to receive those signals, so it was trivial to generate an Email and page from misterhouse when this sensor got triggered.