Mine has metal contacts in the back of the drum, which I presume measures resistance, similar to how this soil moisture sensor works: https://www.adafruit.com/p

Mine has metal contacts in the back of the drum, which I presume measures resistance, similar to how this soil moisture sensor works: https://www.adafruit.com/product/6362 https://www.adafruit.com/product/6362 I'll never understand how modern designs work worse, despite access to better sensors.