MagnetismElectromagnetic Technology |
How do metal detectors work? |
Built into the frame of a metal detector are coils of wire that carry a current. When metal is close to the coils, the magnetic properties of the metal change the current in the coils of wire that is detected by the electronic circuits in the detector.

When you walk through a metal detector with metal anywhere on your person, that metal changes the current in the coils in the frame of the detector.