Review: Sonoff S20 WiFi Plug

The good folks at Sonoff have sent me a bunch of kit to review.
First up, the S20 WiFi Plug - an easy way to retrofit IoT smarts to your existing appliances.

A schematic diagram of a smart plug

This fills the same niche as the Belkin WeMo but with one crucial difference - it's about half the price.

Direct from Sonoff it's US$13 - from Amazon UK the smartplug is £15. The cost of the WeMo is £40.

How does it compare to the Belkin WeMo?

Both are compatible with IFTTT, have 2.4GHz WiFi, and have buttons and status LEDs. The both also have time schedules so you can automate when the plug switches on and off. They basically have identical features - with two small differences.

The WeMo works with Alexa, the Sonoff doesn't. Alexa is still in its early days - but if small companies like WisQo are able to make Alexa compatible light switches, then I would expect the same from Sonoff.

There is a 3rd-Party Alexa skill - called eWeLink Fan. It's not as easy to set up as a normal smart-home device, and judging from the comments on the Sonoff website suffers from some problems.

Where the S20 realy comes into its own is its hackability!


You'll find lots of articles on the web about how to rewrite the firmware in these devices - Nathan Chantrell has an excellent guide on his blog.

The S20 uses the ESP8266 - a ridiculously common WiFi chip. Versatile and hackable. Perfect for tinkering.

There are loads of 2866 projects on GitHub for you to build with. There are several websites dedicated to hacking these controllers.

There are several variations of this plug - so pay attention when following the tutorials.

Finally, electricity is dangerous. Make sure you know what you are doing before you start unscrewing and fiddling.

Security and API

The app uses SSL - so your connection to the Sonoff mothership should be secure. There's no certificate pinning, so your calls can theoretically be intercepted or disrupted. That's still better than most IoT kit.

There is an API available, but it is undocumented. It also needs to go through the manufacturer's servers. I wish more IoT makers would follow Lifx's lead and offer a fully documented API which works over a LAN. I don't don't want to be locked out of my gear if my Internet goes out, or the manufacturer goes bust.

As I've mentioned, these devices are easily flashable - so can be repurposed if needed.


While the hardware is great, the software is a slight letdown.

The Android App doesn't get great reviews - it's quicker to start than the WeMo app, but doesn't look as nice. Registration is a bit complicated, as is sending WiFi passwords.

As with most domestic IoT devices, it's ideally suited to a single person household. It is possible to share control with another user, but it is a little cumbersome.

There's no energy monitoring - although other Sonoff products provide that service.

Finally, is this actually useful? I've only got a few electrical items which I turn on and off from the plug socket - lamps, electric heaters, ... ummm... a hair-drier? I'm using mine on a cool air fan which sits across the room from me.


In terms of speed - this blows the WeMo out of the water. The weird Alexa integration is a minor annoyance - but it makes up for it by being so hacker friendly.

The plug is small and sized well for going on a multi-socket. The software needs an overhaul, but it does the job.

You can buy the Sonoff S20 from Amazon UK for around £15.

Thanks to Sonoff for sending me the review unit. If you'd like me to review your gear, please get in touch.

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3 thoughts on “Review: Sonoff S20 WiFi Plug”

  1. FreeZing says:

    s20 can work with Amazon Echo(Alexa) and Google Home now, so just ask 'Alexa,turn on the socket' , then it will work~ Try it, and s20 will work with Siri soon.

    And the s20 can work with Google Nest as well, you can set the IFTTT mode.


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