Pin Screen Lock

One of the best pin lock screen application in android market.

How it works:

You have to enable lock screen in settings in this application and whenever you unlocks your phone, you will be passed through this keypad lock.

If you do not want pin lock, you can just enable slider lock. There is no way your phone will get locked permanently by using this application. In case you forgot your password, you can press home button and you will come back to main phone screen and unlocked too.