LG D855 Quick Start Manual page 46

Screen
Knock Code
The Knock Code feature allows you to tap the screen with your
own Knock Code pattern using the screen divided by 4 squares to
easily turn the screen on or off. You can disable this feature in the
Lock screen settings.
1. From the Home screen, tap the Apps Key > Settings > Display >
Lock screen > Select screen lock > Knock Code.
2. Tap the squares in a pattern to set your Knock Code.
Your Knock Code pattern can be 3 to 8 taps. Tap Done when
you're finished.
NOTE: When the Knock Code is not in use, you can use Knock On function by tapping the screen.
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