Lock or unlock the keys and screen
To avoid accidentally making a call when your phone is in your pocket or bag, lock the keys and screen of your phone.
Lock the keys and screen 
Press the power key 
.
Unlock the keys and screen
Press the power key or the menu key, and select Unlock.
Set the keys and screen autolock delay
-
Select
> Settings and Phone > Display > Screen/keylock time-out . -
Define how long your phone waits before the keys and screen lock automatically.