EDIT: (2021-09-19): After some back and forth with /u/Laxarus, there is now a simpler method! The snmp platform still does not support setting device_class, but wrapping the sensor in another template sensor is not required; just do so in your customize.yaml. I have called this out below. This is another quick “here’s how I did it, hope this help” post. In preparation for the inevitable grid brownouts that summer 2021 would bring, I installed a rather beefy UPS for my home network / lab.

Update This post is now deprecated. It has been superseded by Using ESPHome with the Treatlife DS03 from 2022-06. UPDATE: (2021-10-22): Tasmota 9.5.0 has been superseded by the new Tasmota 10.0.0 release. This release works perfectly with the rules/automation outlined below; you no longer need to avoid the problematic 9.5 release with the DS03. I am extremely grateful to every one of the people that contributes to the Tasmota project to keep it improving!