What is it?

ESP32-S2 board with a 3xAA battery holder. Ultra low power consumption components. Has onboard temperature and humidity sensor, but just about anything can be connected to it.

Why did you make it?

I need to control for risk of mold in areas that are hard to access and with no power, like crawl space, attic, storage building, etc. I wanted a board to measure temperature and humidity, but also be able to hook up other sensors and functions. I only need to measure once an hour, and sleep the rest of the time, which means this board will run for more than 3 years.

What makes it special?

There are several boards powered by batteries out there, but who knows if you can buy them years from now. This board runs on 3xAA batteries that you can buy in any store. The battery holder makes in solid and no enclosure is needed. This board has "awake power", which means you can hook up other sensors and equipment that will only be powered during awake state. The board comes with code for ESPHome and ready to use with e.g. Home Assistant. You can also upload your own code, a few example codes are available on my Github.