Its price free and also ad free (interstitial ad ) application.
Knock Door Screen Locker is an amazing and simple application for your phone screen locker.

Its keeps you secured from unauthorized from person by door.

By using this application you will get ride entering PIN or Draw specific pattern. you just need tap/knock on your phone's screen with specific(you can adjust in settings) count as pattern or PIN.


Technical Info:
First time after lunch their is no default pattern . Door can be unlocked by any knock count (1,2,3 , etc) .

when you go for activate you need to set knock pattern by knocking door for specific times you want.
note: timer duration between two knocks must be less then 1 second.
and when you ever forget about you knock pattern don't worry , then you can 10 as your pattern.
you can reset or unlock you phone by knocking the door 10 times.

Enjoy Free it with free of cost.