HTC One User Manual page 102

102 Personalizing
2. Tap Screen lock > Face Unlock.
3. Tap Set it up and follow the onscreen instructions.
4. Choose a backup unlock method to use in case the phone doesn't
recognize you.
5. Tap Lock phone after, then specify the idle time before the screen
is locked.
You can also tap Improve face matching on the Security screen to
train HTC One to recognize your face in different situations, such
as when you're wearing glasses or sporting a beard.
You'll be asked to unlock the screen every time HTC One is turned on or
when it's idle for a certain period of time.
To further improve security, select Liveness check on the Security screen.
You'll be asked to blink to unlock the screen.