Keep in mind that:
Follow the onscreen instructions. Be sure to frame your entire face with the outline.
Face matching data is stored securely on the phone.
Whenever you turn on or wake the phone, it will search for your face and unlock the screen 
Show your face to the lock screen.
If it doesn't recognize you, it stays locked and displays one of these icons.
| Icon | How to unlock |
|---|---|
| Use your password, PIN, or pattern | |
| Use the fingerprint sensor |
For increased security, you can require the camera to detect that your eyes are open to unlock with your face.

You can turn on an extra confirmation step for apps that use face unlock.
Turn Always require confirmation on 
Some apps developers may still require an extra confirmation, even if you turn this setting off.
Skip the Power button and just show the phone your face to unlock and go straight to your home screen or last used app. To set it up:

Tap Delete face data.
The phone will no longer recognize your face, and the data is deleted. To turn it on again, set up face matching again.
If you're having trouble getting the phone to recognize your face: