The REV Robotics Magnetic Limit Switch is a three-sided active-low digital hall effect switch with three internal hall effect elements located on the top and sides of the sensor. The three elements are connected in parallel so that any one of them will trigger the sensor.
Hall effect sensors detect the presence of magnetic fields. The REV Magnetic Limit Switch is an omnipolar momentary switch meaning it will trigger when there is sufficient field strength of either magnetic pole (north or south) detected.