The ESP8266 Wifi relay board is a great starter project for the IoT Internet of Things.
Control DC or AC mains devices with the on-board 10A relay from anywhere in the world using your phone or mobile device. As well as a relay, this module also has an isolated optocoupler input for detecting a logic-level signal. In around 10 minutes you can have a working board controlled from an IoT app such as Blynk.
Note: These boards come un-programmed and firmware will need to be uploaded before first use using a USB-serial converter or similar device, plus programming software such as Arduino IDE.
For beginners, you can find information on the internet here:
Two channels: One output, one Input
DC Power supply: 6-28V, protected from over-voltage at 33V.
Relay contacts: SPDT, rated at 10A/250VAC, 12A/125VAC (GPIO4).
Optocoupler input: DC Logic level, protected from over-voltage at 33V (GPIO5).
Relay active, Input active and Wifi status LEDs on-board.
Anti-tracking slots on the rear for mains safety.
Size: 65 x 40 x 20mm.