I'm not sure if you are joking here or not -- but, if you've played with the Kinect on a 360, you'd note that it can recognize your hands, and only when you hold your hands out for a set period of time (2-3 seconds, cannot recall exactly) the Kinect wakes up and begins to allow you to input controls.

I was joking. I failed to locate the correct reference to the Hitchhikers Guide to The Galaxy, but I am sure there is a joke on gesture recognition somewhere in there.