Lenovo A8-50 Tablet - Manual (Page 4)

Deactivating the Display
If you do not need to use your tablet temporarily, you can press the On/Off
button to deactivate the display. Your tablet will then enter standby mode to
save power.
1-4 Screen Lock/Unlock
Screen Lock
Auto-Lock
You can set screen timeout by tapping Settings > DEVICE > Display
> Sleep. If there is no operation within the preset standby time, the display
will automatically deactivate, and your tablet will be locked automatically.
Manual Lock
If you do not need to use your tablet temporarily, you can press the On/Off
button for about 1 second to deactivate the display. Your tablet will then be
locked, and will enter standby mode.
Screen Unlock
When in standby mode, press the On/Off button on your tablet to activate
the display. Then, tap and hold the lock icon, and drag the slider over the
unlock icon, as shown in the illustration below.