Tap Settings > Security and Location > Face unlock. If you don’t have screen lock set up on your phone, tap Set up screen lock.
Select what backup unlocking method you want to use for the lock screen and follow the instructions shown on your phone.
Keep your eyes open and make sure your face is fully visible and not covered by any object, such as a hat or sunglasses.
Note: Using your face to unlock your phone is less secure than using a fingerprint, pattern or password. Your phone may be unlocked by someone or something with similar appearance. Face unlock may not work properly in backlight or too dark or bright environment.
Unlock your phone with your face
To unlock your phone, just turn your screen on and look at the camera.
If there is a facial recognition error, and you cannot use alternative sign-in methods to recover or reset the phone in any way, your phone will require service. Additional charges may apply, and all the personal data on your phone may be deleted. For more info, contact the nearest authorized service facility for your phone, or your phone dealer.