The Apple Watch has a nifty Power Reserve feature that lets you continue to tell time while preserving your battery life. The smartwatch will automatically enter Power Reserve if the battery gets too low, and you might see a red lighting bolt next to the time. However, you can enable the reserve feature manually.
In Power Reserve, press the side button to show the current time in a 24-hour format. The time will display for six seconds. While your Apple Watch is in Power Reserve, your Apple Watch and iPhone won't communicate, and you can't access other watch features.
To turn the watch back on, press and hold the side button until you see the Apple logo and wait for your Apple Watch to restart. You might need to charge your watch first.
If you need to, you can turn on Power Reserve. Press and hold the side button until you see the Power Off, Power Reserve, and Lock Device options. Then drag the slider to turn on Power Reserve.
You can also turn on Power Reserve using Glances. Swipe up on the watch face to open Glances, then swipe left or right to find the Battery Glance. Tap Power Reserve, then tap Proceed.