ESP-WROOM-32 on a selfmade PCB-layout with an BME280 sensor. Powered by an 1W 6V Solarcell and a 2000mAh LiPo Battery.
The device is up for 1300ms and sleeps 10 minutes.
The current while sleeping is about 11µA and at uptime about 100mA.
Using an ESP8266 ESP-01 module and an Arduino Pro Mini 3.3V I wirelessly update all outputs from my thermostat to here for data analysis and because it's cool.
This requires a voltage divided rectifier since thermostats run at least 24 VAC RMS.