An electromechanical differential motion sensor is disposed to detect transverse motion of a first piece relative to a second piece. The sensor includes a base anchored to the first piece, a lever arm that engages the second piece, a hinge, a retention mechanism, and a fuse wire. The hinge connects the lever arm to the base, such that the lever arm rotates relative to the base when the second piece displaces laterally with respect to the first piece. The retention mechanism retains the electromechanical differential motion sensor in a closed position wherein a first jaw of the base is aligned with a second jaw of the lever arm. The fuse wire carries an electrical signal current, and extends through the jaws such that transverse motion of the second piece relative to the first piece deflects the sensor from the closed position to an open position, thereby severing the first fuse wire.