Monitor chain link gates, safes, walk-in freezer, doors, etc. These rugged industrial contact sensors are triggered by the proximity of a magnetic field (magnet included). They are weather resistant and offer a wide temperature operating range. They come with a 36" armored cable to resist vandalism.
The GRI-4402-A offers SPDT form C contacts so they can be used in open or closed loop circuits.
More information is available on the website of ControlByWeb.