A stock Zigbee door/window sensor, with its Hall-effect chip desoldered and two wires brought out in its place, becomes a cheap, battery-powered interface for any simple contact — reed, pressure pad, or float switch. Built to stop Home Assistant from switching off the office lights while sitting still at the desk; the same trick already covers a toilet tank float and a Christmas tree water level.

A 3D-printed clip mounts a submersible float switch on a toilet tank’s overflow tube and wires it into the same desoldered-Hall-effect Zigbee mod used for the office chair sensor. The result: Home Assistant catches a stuck fill valve before it turns into a running toilet, and gets a flush count for free.