A lighting circuit detector has been designed, with an aim to detect different load types of lighting wiring, and reduce the potential risk of electric shock accidents from random construction. The detector, based on the principle of electromagnetic induction, incorporates the giant magneto-resistance as the basic detection device, and improves the circuit of amplifier and filter to realize the collection of the signal. With STM32 its processing units, the detector has undergone an FFT transformation for the collection of signals, followed by a spectrum analysis to realize lighting wiring between different load types. After repeated experiments, the obtained results show that the designed circuit can make a distinction between the efficient light-bulbs and the filament lamps within the scope of 3~4 cm and identify the presence or absence of the circuit load.