This is a cool app for those who have an OLED display with Android ( Most of Samsung devices have AMOLED screens ). For you there is a new app in town, Knockr. This is an app with Motion Launch actions.
This new app lets you set actions for double taping, long pressing, swiping to the right or left, up or down. The best of them is the volume up rocker to launch the device's camera app when having the camera on portrait mode, all from a screen-off state. The thing is that when you turn Knockr on, the Power button won't turn your phone on as you would expect it and the LED notifications won't work. You can set Knockr to turn off when you put the device in your pocket or it is facing down.
Another thing is that when you install the app, you shouldn't have the lock screen security code enabled. You can't bypass the PIN code with any gestures. This may be the biggest issue of this app. Have you used motion launch gestures ever? Do you have any favorites? This app is pretty cool to use.