The Wi-Fi-based smart switches and plugs you can buy contain a mechanical relay that activates when the microcontroller receives a binary input, such as 0 or 1, usually sent via an app. These devices only allow you to control the on/off status of devices, such as a fan, motor, or light. If you also want to control the speed or the brightness of the connected AC mains appliance or load, you will require a TRIAC-based solid-state relay switch.