The present teaching relates to a magnetic sensor that comprises a housing, an input port and an output port, both extending from the housing and the input port being connected to an external alternating current (AC) power supply, and an electrical circuit. The electrical circuit comprises an output control circuit coupled with the output port and configured to be responsive to a magnetic induction signal to control the magnetic sensor to operate in a state in which a load current flows through the output port when a predetermined condition is satisfied, and operate in another state when the predetermined condition is not satisfied. The operating frequency of the magnetic sensor is positively proportional to the frequency of the external AC power supply.