SONOFF S31

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

Compatibility snapshot

Why it stands out

• energy monitoring built in — track power usage per device
• easily flashable to Tasmota or ESPHome for fully local control
• compact form factor that does not block adjacent outlets

Reasons to hesitate

• stock eWeLink firmware is cloud-dependent — flashing is recommended
• flashing requires opening the case or using a serial adapter
• no Matter or Thread support

Best for

• Home Assistant tinkerers who want cheap energy-monitoring plugs with Tasmota
• anyone comfortable flashing firmware for the best local-control smart plug value

Avoid if

• you want plug-and-play local control without flashing firmware
• you are not comfortable opening devices or flashing custom firmware

Privacy and local-control notes

Flashable to Tasmota or ESPHome for fully local, cloud-free operation. Stock firmware uses eWeLink cloud.

Home Assistant support: supported · integration path: Tasmota / ESPHome / eWeLink.

Built with ESPHome — see our ESPHome guide for Home Assistant →

Buying reality check

Price notes: One of the cheapest energy-monitoring smart plugs available. Incredible value when flashed to Tasmota.

Compare side by side: see plug comparisons →