Turning the screen on using the Knock Code feature
If your Lock screen unlock sequence is set to a Knock Code, tap your Knock Code on the darkened screen to automatically turn the screen on and unlock it at the same time.
TIP!
When the screen is in time-out and a Knock Code
is set, pressing the Power/Lock Key 
(on the back of the
phone) displays the Lock screen (e.g., to check the time). You can
tap your Knock Code to unlock the screen or turn the screen back off
by pressing the Power/Lock Key again (or double-tap
the Status Bar).
NOTE
Entering the incorrect Knock Code 6 times will prompt you to enter your backup PIN to unlock your phone.
Use a fingertip instead of a fingernail to tap the screen to turn the screen on.