regardless of skill with a soldering iron or Arduino toolkit. So they decided to base the guts on common components that can be put together easily, specifically a Wemos Mini D1 with an OLED ...

You have an ESP8266 board like the Wemos D1, a Li-Ion battery ... learn a few tricks for doing sleep Arduino environment, and even calculate how long your specific battery could last.

In summary, the D1 Wi-Fi introduced here is a ESP8266-12E Wi-Fi board, similar to the good old WeMos D1 R1 board that uses the Arduino Uno layout ... We can see only the belittled D1 mini, D1 mini ...