The Redmi Watch 4 has a Power Button. For your reference, here is more information about how to turn on, turn off and restart the watch :
1. In the power-off state, press and hold the Power Button or connect the watch charger for about 5 seconds to turn on the watch and enter the home screen;
2. In the power-on state, press and hold the Power Button for 3 seconds, and the watch will enter the page of reboot, power off and restore factory, which you can select as you prefer;
3. In the power-on state, tap [Settings] >> [System] >> select [Power off] to turn off your watch;
4. In the power-on state, tap [Settings] >> [System] >> select [Reboot] to restart your watch;
5. In the power-on state, keep pressing and holding the Power Button for about 12 seconds, the watch will be forced to reboot.