Abstract: A motion detector particularly adapted for use with the transmitter of a motor vehicle keyless entry system. The motion detector causes the transmitter device carried by the user to transmit a coded signal when it is in motion, for example, as it is being carried by a user toward the vehicle. The motion detector includes a spool surrounded by and electrically insulated from a shell. A ball is positioned in the annular cavity around the spool. Associated electronics are provided to sense a change in state of the motion detector as an indication of motion. Changes of state of the motion detector occur when the ball moves into and out of direct contact with the spool or shell and further as the ball rolls around the annular cavity while being supported by both the spool and shell caused by surface roughness of the interface surfaces.