1. A method, comprising: receiving, by a computer executing a non-tactile three dimensional (3D) user interface, a set of multiple 3D coordinates representing a gesture by a hand positioned within a field of view of a sensing device coupled to the computer, the gesture comprising a first motion in a first direction along a selected axis in space, followed by a second motion in a second direction, opposite to the first direction, along the selected axis; and transitioning the non-tactile 3D user interface from a first state to a second state upon detecting completion of the gesture.