You have an ESP8266 board like the Wemos D1, a Li-Ion battery, you want to build a small battery-powered sensor that wakes up every few minutes to do something, and you don’t want to delve into ...

Living in a condo with inadequate opportunity for fresh light wiring presented a problem for [Raphael Luckom], which he solved by taking a few off-the-shelf ESP8266-based IoT mains switches.