Provided herein are approaches for detecting movement of a seatbelt sensor. In some approaches, a detector includes a sensor housing coupled to a plate of a vehicle restraint system, and a sensor disposed within the sensor housing, wherein the sensor is operable to sense a position of a magnet in proximity to the sensor. The detector further includes a magnetic field accumulator (e.g., a pole-piece) coupled to the sensor, wherein the magnet and the magnetic field accumulator move relative to one another, and wherein the sensor receives an indication of a magnetic field accumulated by the magnetic field accumulator as the magnet and the magnetic field accumulator move relative to one another. A change in the magnetic field distribution correlates to a change in position of the plate, to which the magnet is coupled.