This app will unlock the free version. Please keep the free version installed. https://play. google.com/store/apps/details? id=com. jamworks. knockzWith KnockOn you can easily wake or lock your phone with a simple double tap on screen. MAIN FEATURES: Tap to lock your phone. Tap to wake your phone (OLED displays only). Both features can be activated separately. Set up a sleep time to reduce power consumption. Customize double tap speed. No annoying ads.