For a long time I’ve wanted to make some temperature sensors that report real-time or near enough temperature readings. It’s been done a lot before but not by me! My requirements are:

* As cheap as possible - I’d like to make lots of them
* Weatherproof so they can be outside
* Very power efficient so they can run on battery power
* Long battery life to avoid having to service them too often
* Backhaul measurements with GSM or maybe WiFi - again to avoid having to collect data physically

I think I’ll base it around one of the relatively new ATtiny1616 microcontrollers since they have impressively low power consumption. For power, I suspect a lithium cell will be needed to provide plenty of power for a long time, while still coping with the high current spikes demanded by a GSM module.