Lock your Android phone automatically after its screen turn off. This action can be done immediately or after from 5 seconds to 30 minutes. Samsung Galaxy owners like S3, S2, Ace needs to follow these steps to customize lock screen timeout:
1. Open "Settings" app and go to "Accessibility"
2. Tap "Lock Automatically"
3. Choose Immediately so the phone screen locks as soon as screen turns off. or from 5 seconds. You may also define a time gap from turning off the screen to locking the screen (This time can be set from 5 seconds to half an hour)