Sony SGPT21 - Manual (Page 67)

Locking the Screen
You can lock the screen of your tablet device to prevent accidental touching of the screen from activating
operations.
If you activate the lock function, the screen is locked when the screen is turned off. You can also select how to
deactivate locking.
To configure the lock function
1. Tap [ Apps] - [ Settings] - [ Location & security] - [Configure lock screen] in that order.
2. Tap the desired setting.
3. Follow the on-screen instructions.