Quick verdict
The S31 is the cheapest path to energy monitoring smart plugs that actually work locally. Flash it with Tasmota or ESPHome and you've got a fully local plug with power tracking. Stock firmware is cloud-dependent, so plan on flashing — it's easy and well-documented.
Standout: Budget energy-monitoring smart plug that is easily flashable to Tasmota for fully local control.
Last checked: 2026-03-22