Unlock by tapping the screen
KnockOn is a handy app to quickly unlock your Android device without using the power button. A double tap is enough to awaken your smartphone and, in the same way, you can lock it again. The concept is not new but works well.
Keep in mind that the “Wake on tap’ feature consumes much energy on devices that do not have an AMOLED screen. KnockOn makes the picture namely completely black, but in non-AMOLED displays the black pixels are still lit. The ‘Lock on tap’ function is energy efficient, whatever screen type you have.
If you have set a Security Code or pattern, then you must also enter that just after activating KnockOn to access your smartphone. However, the double-tap to wake function is handy to have a look whether you have received any new messages.
Download KnockOn for Android
Via the link below you download the free version of KnockOn which requires at least Android 4.1 and 0.5MB of free space. The paid version ($1.20) lets you enable a sleep mode and determine how fast you must tap to unlock your device.