I’ve been making these inexpensive BLE sensors using Nordic nRF51822 modules that are really common on ebay/Aliexpress. I have some examples of simple door/window sensors, as well as more advance window sensor that reports how much the window is opened. I also use WiFi gateways to do some geolocation, tracking what rooms my dog hangs out in. All this data bridges over to MQTT, so it’s really easy to use in OpenHAB. I’m using really inexpensive parts, and the development IDE is ARM MBED, which is easy to get going with.
Wow that’s a really good write up. I’d played with bought ble beacons and blue maestro tempo disks where I was reading Bluetooth advertisement packages, But you’ve taken that to the next level.
So the main premise is that you can buy then ble beacons and modify their code and attach other sensors on them to make low cost sensors. Easier than the d1 mini with a sensor and requiring power.