US Patent 10488464 Magnetic sensor circuit for security sensing

A sensor circuit for sensing a circuit change, e.g. circuit break, is described. It comprises a permanent or electro magnet for generating a magnetic field, a sensing system comprising one or more magnetic sensors configured for sensing an at least one dimensional magnetic field from the permanent magnet and for providing an output signal representative of said at least one dimensional magnetic field. The circuit also comprises a controller for detecting an event by comparing said output signal with reference data, said reference data comprising for at least one direction of said magnetic field a reference range having an upper boundary and a lower boundary wherein the upper boundary and lower boundary are magnetically unipolar.