A motion detector comprising a rotator member having at least one radially positioned member and being mounted for rotation from at least a first position to at least a second position; a detector member, preferably a Hall Effect sensor; and a magnet producing a magnetic field; wherein, the radially positioned member is characterized by altering the magnetic flux of the magnetic field when it moves into and out of proximity to the magnet; and wherein the detector member detects the alteration of the magnetic flux. The motion detector is preferably used to detect the speed, type, position, presence, and absence of a printer ribbon cartridge.