I know this is an old question - but here is an answer if anyone finds it in a search:
Google GS-WDS07 - they are a cheap 433mhz reed switch, battery operated with open/close, tamper and low battery alerts. The circuit board is small enough to stuff into lots of enclosures and they operate for ages on a AAA battery.
I use them for various things (including as door/window sensors). If you unsolder the reed switch off the board, you can connect an external switch that will send a signal for open and close events. The tamper switch is usually unpopulated - you can solder in another switch to these contacts but it only will signal on circuit closed, you can get around this by using a dummy value for circuit open (off) and use as a momentary switch.
Of course for any of this to work you will need a 433mhz to wifi bridge, like the Sonoff bridge