Turning the screen on using the KnockON feature
The KnockON feature allows you to double-tap the screen to easily turn the screen on or off. You can disable this feature in the Gestures settings.
Quickly double-tap the center of the screen to turn the screen on.
Quickly double-tap the Status Bar, an empty area on the Home screen, or the Lock screen to turn the screen off.
NOTE
The KnockON feature can be turned off in the Gestures menu. From the Home screen, tap Apps
> Settings 
> Gestures > tap the KnockON checkbox 
.When turning the screen on, make sure you do not cover the proximity sensor. Doing so will not allow you to turn the screen on.