HTC One SV User Manual page 52

52 Personalizing
4. Choose a backup lock 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
SV 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 SV 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.