@jamzm what are you looking for in particular?
I use a ProMini with the Door/Window/Button switch. The sketch is modified to always sleep and wake up on change. (https://www.mysensors.org/build/binary), with a reed switch (https://www.aliexpress.com/item/32468849883.html?spm=a2g0s.9042311.0.0.27424c4dYn4UwZ)
The sensor is powered with two AAA batteries. The case is actually from a real door/alarm system from aliexpress which I first wanted to hack but then decided to strip the electrnics out and build it myself. I use a NC reed switch to save additional power (when door is closed mainly).
If you are interested more in the other part of my answer, I use OpenHAB as a controller. I have extensive rules to react base on an "uncontrolled" opening of a door or window.
This could be anything from turning lights on to send an email to your phone, triggering an external security company or enabling your sprinkler ;-)
