Using a Screen Lock
Set a screen lock to secure your phone and prevent unauthorized use.
From the Home screen, tap the Menu key
> Settings > Lock screen > Select screen
lock, then select your lock type (Pattern,
PIN, or Password).
If you choose Pattern, you'll be prompted to create a Backup PIN as a safety measure in case you forget your unlock pattern.
Sign in to (or create) a Google Account before setting a screen lock (and remember the Backup PIN you created when creating your screen lock) to reduce the risk of needing to perform a Hard Reset which erases all of your data.
It's very important to remember the screen lock you set. After five incorrect attempts you'll be prompted to enter a phrase to verify that you're trying to unlock your phone. The phone will automatically reset itself and erase all of the phone's data after ten incorrect attempts.