Home Automation

This sounds similar to what I'm setting up, although long term I'll have more than just temperature sensors. I decided to "roll my own" to avoid any reliance on servers which might suddenly disappear, and went with ESP8266-based modules, using DS18B20 sensors which are very easy to get working. I've also hooked in a light sensor using an LDR on the analog input, as I want to automate my lights as well.

The ESP8266 (and ESP32 mentioned by CaptainFuture) has built-in WiFi so can connect to your local router. I decided on MQTT as a messaging protocol, as it's very simple and designed for exactly these kinds of application, and I'm running Node-RED on my server to handle all the logic and the UI. Again, very easy to use and a lot quicker than hand-coding it all. Below I've added one of my dashboard pages and one of the Node-RED flows running it all, to give you an idea of what's possible.

 

Thanks - those things look much more complex than I was imagining - that's why I mentioned Bluetooth-LE - the ideal device for me would be something with the form factor of an Tile / AirTag tracker - something that'll run for ages off a single button cell, that I can just blutack somewhere and basically forget about it (until its battery needs changing)

Such things definitely do exist but, as with you, I really don't want something that wants to integrate into third party apps and servers - Ideally I'd like something fully open (or as open as you can be when dealing with bluetooth protocols)