This video also answers some of the queries below.
double tap app
double tap on screen to wake up android.
double tap screen on and off apk
double tap screen two wake apk
double tap to unlock android apphttps://play.google.com/store/apps/details?id=com.kimcy929.doubletaptoscreenoff&hl=en
Install and open this app called "double tap to lock". Now enable "double tap". Select "Activate" and then enable it again. Now you need to enable double to screen off. OK. Again enable here. Go back. Now you need to enable double tap to screen on. OK. Scroll down. You can select start on boot so that this application starts when you restart your android device. Now you can go to number of taps to screen off and from here you can select "Double tap". The default you can see is Triple tap but we want to make double tap. So, once you do this one let's go back to the home screen and lets tap two times on the home screen. Now you can see that the device is locked. Now if you want to unlock the device just tap twice on the screen. and you can see the screen is on. So, this is how this application will help you to switch on, switch off the screen without pressing any physical button on your android device.