This is the Sonoff Pow - a WiFi enabled in-line power switch.
Wiring up the Pow is relatively easy. The cover to the terminal block is secured with a simple screw.
I found the opening a little cramped - but it's easy to open up the entire unit. Which gives us a full view of the circuitry.
There's an unpopulated header on the bottom left - yup - this thing is hackable!
A reminder, working with electricity is dangerous - if in doubt, consult with a trained professional.
The latches on the terminal block are stiff, but that's probably a good way to stop the leads from falling out.
Once wired up, and power applied, the LED starts flashing.
From there, you can install the Android app and connect the Pow to your WiFi.
If you splash out, you can buy the Sonoff G1 - which has a GSM modem built in. Add a SIM card and it will connect to GPRS. Only $20!
As with other Sonoff products, this is built on the ESP8266. As the manufacturer says:
Apart from traditional consumers, Sonoff Pow is a very exciting product for those into hacking, since four program ports have been reserved for burning external firmware. Now, isn’t that thrilling?
There are a range of firmwares available on GitHub, and YouTube videos showing how to take control of the device. There's a burgeoning community of bloggers with some great tutorials - see Tinkerman and CNX Software.
As with the S20 plug, this is a great little unit. It's easy to set up, the app works reasonably well, and it is dead cheap.
The power monitoring seem fairly accurate - it picked up the exact wattage of my lightbulb - and the timers worked.
As with the S20, its usefulness depends on the electronics you have at home. If you have devices which regularly need turning on and off from the mains, this is perfect. The addition of monitoring makes it useful for anyone energy conscious.
The app is adequate - not brilliant. There's no public API - which is a shame - but you can rewrite the firmware if that bothers you.
Amazon's Echo Smart Home doesn't work natively with the 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.
If you're handy with wire strippers, it's a great little gizmo. Ideally it would be built into appliances - but as a way to add IoT smarts to an old device, it's pretty good buy.