Turn it on, then the screen will stay on when your face is detected by the front camera. You can go to Settings>Smart motion>Smart turn on/off screen to turn it on.
Warmly Tips: This function may not work in the following situations:
1. You are not facing the screen;
2. The front camera is blocked;
3. You are using it in strong light or a dark place;
4. The front camera is used by another app.