There are two physical buttons at the right of the Xiaomi Watch S4. The upper one is Rotating Crown, and the lower one is Power Button.
To power on, power off and reboot the watch, please refer to the following details:
1. Power on: When the watch is powered off, press and hold the power button for 3 seconds to enter the homepage of the watch;
2. Power off:
(1). Press and hold the power button to enter the interface of Reboot, Power off, Connect new phone, and Factory reset, and tap [Power off] to power off the watch;
(2). When the watch is powered on, go to [Settings] >> [System] >> [Power off].
3. Reboot:
(1). Press and hold the power button to enter the interface of Reboot, Power off, Connect new phone, and Factory reset, and tap [Reboot] to reboot the watch;
(2). When the watch is powered on, press and hold the power button for about 12 seconds to force reboot the watch;
(3). When the watch is powered on, go to [Settings] >> [System] >> [Reboot].