Magnetic sensors detect only magnets; but, have several advantages. Detection distance is one. These are offered with reed relays up to 3 amps, thus eliminating the need for interposing relays in many applications. For faster response, we also offer units with PNP or NPN outputs. Great for over/under speed monitoring. Then some special units that will only respond to the South Pole of a magnet, others the North Pole and still others latch upon detecting the South Pole and unlatch in the presence of the North Pole. Read all about these amazing sensors by clicking on How They Work.