AH1801 is a Micropower, Ultra-sensitive Hall Effect Switch, which is with two Hall effect plates and a output driver, mainly designed for battery–operation, hand-held equipment (such as Cellular and Cordless Phone, PDA). The total operation power is down to 24uW in the 3V supply. Either north or south pole of sufficient strength will turn the output off. The output will be turned on under no magnetic field. While the magnetic flux density (B) is larger than operate point (Bop), the output will be turned off, the output is held until B is lower than release point (Brp), then turned on.