A metal detector is an electronic instrument that detects the presence of metal nearby. Metal detectors are useful for finding metal inclusions hidden within objects, or metal objects buried underground. They often consist of a handheld unit with a sensor probe which can be swept over the ground or other objects.

Different metal detectors work in various different ways, but here's the science behind one of the simpler kinds. A metal detector contains a coil of wire (wrapped around the circular head at the end of the handle) known as the transmitter coil. When electricity flows through the coil, a magnetic field is created all around it. As you sweep the detector over the ground, you make the magnetic field move around too. If you move the detector over a metal object, the moving magnetic field affects the atoms inside the metal. 

Generally, there are many buttons on the panel of a metal detector. Buttons include tuning buttons, sensitivity buttons, identification buttons, etc. Of course, the mode button and power button are also indispensable.

Due to the wide variety of metals underground, some instruments have the function of distinguishing specific metal types. Therefore, the designer will put the words "GOLD", "SILVER" and "BRONZE" on the panel to facilitate users to distinguish metal types.