This app alows you ONLY to lock device. Unlock feature is available in my other app - Knock Unlock (beta, may not work properly) (https://plus.google.com/communities/102983045850460117969)

Knock Lock is simple application that allows you to select area on your display to enable "knock to sleep" feature. Also in app you can select size of area available for knocking.

- How does it impact battery life?
App does nothing other than creating small area for knocking. Battery usage should be below 0.1%.

- How to uninstall this app?
Remove access to service that you have selected at start. You can do this by clicking button in app again and selecting "device admin" section or by going to Android settings -> security -> Device Admins. Then you can uninstall app.

-Why there is visible notification?
This notification is part of Android responsible for keeping app alive all time. You can hide it in Android app settings (there is option to hide app notifications from showing).

If you have problems with app or want to ask question, email me from this app page.