An apparatus for sensing relative positions of mechanically coupled devices. The apparatus includes a magnetically actuated switch connected to a set of flux conductors to form a switch assembly. A permanent magnet is affixed to a set of flux conductors to form a magnet assembly. The flux conductors are positioned adjacently to conduct flux from the permanent magnet to the magnetically actuated switch. Movement of either assembly results in the reduction of flux conduction between the magnet and the magnetically actuated switch. The apparatus can be integrated into a helmet mount for night vision goggles to sense the relative position of the helmet mount for controlling the operation of the night vision goggle.