LG M700n Mode D'emploi page 54

KnockON
You can turn the screen on or off by double-tapping the screen.
This option is available only on the Home screen provided by LG. It may
not function properly on a custom launcher or on the Home screen
installed by the user.
When tapping the screen, use your fingertip. Do not use a fingernail.
To use the KnockON feature, make sure that the proximity/light sensor
is not blocked by a sticker or any other foreign substance.
Turning on the screen
Double-tap the middle of the screen.
Tapping the top or bottom of the screen may decrease the recognition
rate.
Turning off the screen
Double-tap on an empty space on the Home screen and Lock screen.
You can also double-tap an empty space on the status bar.
Basic Functions 53