How does a metal detector actually detect metal?

Most people have a general idea of how a metal detector works. You or your stuff goes through a detector, and if there's metal, it will make a beeping sound. But have you ever wondered how, exactly, a metal detector is able to detect metal? The answer may surprise you.

Metal detectors work by using a process known as electromagnetic induction. Essentially, they emit a low-frequency electromagnetic field that penetrates the the body, bags and clothes. When the field comes into contact with a piece of metal, it produces a corresponding magnetic field. This change in the magnetic field is then detected by the metal detector, which emits the familiar beeping sound.

Another way to think of it is metal detectors are basically radios tuned to a very specific frequency. When the detector comes close to metal, it disrupts the radio signal and causes a blip on the screen.