Thanks, this is interesting. Seems like it would be quite cheap to cobble together an ESP32 + cheap sensor. How would you power it - battery or solar? Any estimates of battery runtimes I could get if it woke up every 4 hours or so?
Mostly got them to learn about bluetooth and wrote (half a) daemon to log the packets, currently it just prints the data to cout.
I don't have any estimates of battery runtime or anything, but I'll note that WiFi is battery-expensive and takes a few seconds to actually connect to the desired network so you'll want to wake WiFi as little as possible. Meanwhile, actually doing sensor readings can be done pretty often. So it's entirely feasible that you might do a bunch of sensor readings and then upload them all in one go to save power. From there on out it's a question of how much power a sensor draws, how much power the device draws, and how often you want to wake it.
Ive gotten away with as small as a 6v solar panel 3.5W to keep a box online for 6 months solid.