An apparatus for measuring a strength of a magnetic field, including a switch including contacts configured to change position when a switching threshold is reached, wherein the switching threshold is reached by modifying an external magnetic field around the switch, and a coil wound around the switch, wherein the coil is used to modify the external magnetic field, wherein a first current is driven through the coil wound around the switch until a first switching threshold is obtained, wherein a second current is driven through the coil wound around the switch until a second switching threshold is obtained, and wherein a value of the first current when the first switching threshold is reached and a value of the second current when the second switching threshold is reached are used to determine the strength of the magnetic field.