The Sonoff Basic R4 is a smart relay switch and the new version of the Sonoff Basic R2, the entry-level member of Sonoff's internet-controlled relay switches. As a new feature, it is also compatible with Sonoff's eWeLink-Remote remote controls (Sonoff S-MATE / S-MATE2 units, R5 wireless switch). It is a relay switch unit with WiFi + Bluetooth support, requiring 230V AC power supply and can be used to turn electrical devices on/off. Using an app running on an iOS (Apple) or Android mobile phone connected to the internet, you can remotely control the switch and set a scheduled on/off. Naturally, there is also a physical button switch on the relay. And the remote access capability via the mobile app can be shared with family members. Ideal for smart control of household electrical devices that do not need to be constantly on but need to be turned on/off intermittently (e.g., aquarium circulator or aerator). It can be used for the convenient remote activation of devices before you arrive home, and it can also be used for convenient time-off to save energy and money.