This board is essentially a Wi-Fi controlled relay that you can trigger with an App from anywhere in the world (requires configuration of modem and knowing your modem IP address). Ideal for home automation, IOT (Internet Of Things), lighting control projects, and much more. The board measures just 45 x 28mm and features an ESP8266 module and microcontroller, screw terminal blocks to make wiring easy, and a 5V relay to control power to devices that draw more current than an ordinary development board can handle. A 4-pin header enables you to provide 5V power directly or to connect to the TX and RX serial port debug pins.