Trusted Face

Your phone will trust nobody else

Trusted Face locks and unlocks your phone based on facial recognition.
Check your Smart Lock settings. You will see a warning screen reminding that Trusted Face is not as secure as passcode. Tap Next. Choose a well-lit place, with good indoor lighting (not too bright), look at your screen and move it until your face is inside the orange oval on your screen.
Hold your device steady. When your Android device has finished scanning your face, all the dots will turn green and a check mark will appear.
If your device is not in a Trusted Place or paired with a Trusted device you will see a face icon on the bottom of your lock screen to let you know trusted face will open it. Hold your phone at eye-level and wait for the unlocked icon to appear.
With Trusted Face activated you can interact with your notifications and you phone or tablet will attempt to match your face and unlock without causing you any interference. If you want to unlock it before it has identified you, your lock screen will slide the security input up instead of attempting to identify you with Trusted face.

SMART LOCK SETTINGS
LG G4
In the Security settings make sure Smart Lock is enabled as a Trusted Agent. All other Lock Screen and Smart Lock settings can be found in the Lock Screen settings.

Samsung Galaxy S6 and S6 Edge
The Smart Lock settings can be found by going into the Lock Screen and Security and then into the Secure Lock Settings submenu.

HTC One M9
Smart Lock settings are found directly in the Security menu within the phone's settings just like in the screenshots provided.