Sonoff S31 WiFi Smart Plug Review: The Budget Plug DIYers Love to Flash
A low-cost 15A energy-monitoring plug that many owners run for years, popular with Home Assistant and ESPHome tinkerers, though first-time Wi-Fi pairing trips up some buyers.
The Sonoff S31 is a compact Wi-Fi smart plug that pairs real energy monitoring with a genuinely low price, and it has built a following among DIY and Home Assistant users who flash it with ESPHome or Tasmota for fully local control. Long-term owners report years of trouble-free operation, and the built-in power monitoring is repeatedly praised for tracking appliances like freezers and holiday lighting. The main friction point is initial Wi-Fi pairing through the eWeLink app, which trips up some buyers on 2.4GHz-only networks. For anyone comfortable with basic smart home setup, or willing to flash custom firmware, it is a dependable and inexpensive way to monitor and control an outlet.
- Home Assistant users
- ESPHome and Tasmota tinkerers
- Budget buyers
- Appliance energy monitoring
Pros
- Real-time energy, current and voltage monitoring with 100 days of history
- Handles up to 1800W/15A loads
- Popular with Home Assistant, ESPHome and Tasmota users for local control
- Reported to run reliably for years across many units
- Low price for what it offers
Cons
- 2.4GHz Wi-Fi only; some routers with band-steering cause pairing failures
- No Apple Home, SmartThings, Matter, Zigbee or Bluetooth support
- Minimal included setup instructions
- No USB charging ports
- Not weather-resistant, indoor use only
Who is the Sonoff S31 for?
Owners use this plug to monitor freezers and refrigerators for power draw while away from home, automate holiday lighting, and add basic remote control to otherwise dumb appliances. It is especially popular with Home Assistant users, who connect it through the Sonoff integration, and with DIY tinkerers who flash it with ESPHome or Tasmota to get fully local control without relying on the manufacturer's cloud app.
What buyers love
The most consistent praise is for the plug's built-in energy monitoring, which owners use to confirm an appliance is drawing power correctly or to track consumption for lighting and small devices, matching its supported energy-monitoring feature and its ability to log real-time power, current and voltage. Long-term durability comes up often, with some buyers running more than a dozen units for years without a failure. The plug's compatibility with custom firmware (ESPHome, Tasmota) is a standout for privacy-minded and technical buyers who want to avoid routing commands through the cloud, and Home Assistant integration is called out as smooth.
What to know before you buy
This plug only supports 2.4GHz Wi-Fi, and several reviewers ran into pairing failures because their router's access points were pushing devices to the 5GHz band or otherwise handling band-steering in a way the eWeLink app's setup flow didn't handle well. The included instructions are minimal, which compounded the issue for a few buyers. It also lacks Apple Home, SmartThings, Matter, Zigbee and Bluetooth support, so it is Wi-Fi only and best suited to Alexa, Google Home, IFTTT or Home Assistant setups. There is no USB charging port and no weather resistance, so it is an indoor, single-outlet device.
Is the Sonoff S31 worth it?
At a low price point with a 1800W/15A rating and real energy monitoring, the S31 punches above its cost, especially for buyers who value Home Assistant compatibility or the option to flash custom firmware for local control. Sentiment from long-term owners is strongly positive on reliability, and the main drawback, occasional Wi-Fi pairing friction, is a one-time setup hurdle rather than an ongoing issue. It is a solid pick for budget-conscious buyers who want more than a basic on/off switch.
Frequently asked questions
Does the Sonoff S31 monitor energy usage?
Yes, it tracks real-time power, current and voltage and stores up to 100 days of usage data and total cost.
Does it work with Home Assistant?
Yes, it integrates with Home Assistant, and it is also a popular choice for flashing with ESPHome or Tasmota for fully local control.
Does the Sonoff S31 support 5GHz Wi-Fi?
No, it only connects over 2.4GHz Wi-Fi. Routers that push devices to 5GHz or use aggressive band-steering can cause pairing issues.
Does it work with Apple Home or Zigbee?
No, this model does not support Apple Home, Matter, Zigbee or Bluetooth. It works with Google Home, Alexa, IFTTT and Home Assistant.
What is the maximum load the Sonoff S31 can handle?
It is rated for up to 1800W and 15A.










