If you don’t use the phone for a while, the screen and backlight will turn off to conserve battery power. To unlock the phone’s default Lock screen:
The default Lock screen simply locks the screen to prevent unintentional actions. For more security to guard against unauthorized use, you can set an unlock requirement (such as a Knock Code, pattern, PIN, password) that will need to be entered to unlock it.
Turn the screen on.
Press the Power/Lock Key (on the back of the phone).
Avoid covering the proximity sensor when turning the screen on. Doing so, immediately turns the screen off.
OR
Quickly double-tap the center of the screen (KnockON).
From the center of the screen, swipe in any direction to unlock it.
To use a shortcut, swipe the shortcut icon (at the bottom of the screen) in any direction. The screen will unlock and launch the app.