The way this works is you swipe your hand in the air over the phone to perform an action. You can swipe in any direction, but swiping left or right seems to work best. I originally planned to remap each direction separately, but found this was too unreliable to be practical for most.
Motion Sense must be enabled in System Settings, and the "Reach to check phone" option must be enabled, or this won't work.
The motion gestures will work with the screen off, on the lockscreen and on the homescreen. The sensor is not active within other apps.
For non rooted devices, requires one-time adb setup to allow Button Mapper to read logcat output.
Rooted devices can work right away.
Turn on screen: For rooted users, there is an option to turn the screen on before performing an action.
Play sound on action: Makes a sound whenever a swipe action is performed. This is helpful to indicate that the swipe was detected, especially when the screen is off.
Disable while music is playing: This will stop Button Mapper from performing the assigned action while music is playing. This allows you to continue using the built-in previous and next track gestures while listening to music. When not listening to music, Button Mapper will resume remapping.
A good way to test this out is to assign the "Toggle flashlight" action. It's a quick visual to help you get a feel for how the motion sensing works.
XDA Labs (always latest version)
Note: Many users will not yet find the latest Button Mapper 1.40 on the Google Play Store. Download from XDA Labs if you can't wait.