The M5Stack RELAY as it says is an M5Unit that implement a Relay functions. Relay can be used as an electrically operated switch, uses an electromagnet to mechanically operate a switch, where it is necessary to control a large power load circuit by a separate low-power signal such as digital signal output from a microprocessor. The Relay support input voltage of up to 30V DC and 220V AC. There are 3 pins named: ON, OFF, COM. You can program to make COM connect to ON or OFF, just by high and low out put of a digital GPIO.

Single-BUS control
Up to 3A @ 30 V DC or 220 V AC
Sof tware Dev elopment Platf orm: Arduino, UIFlow (Blockly, Py thon)
Two Lego-compatible holes