A metal detector is an electronic instrument which detects the presence of metal nearby.They 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.
If the sensor comes near a piece of metal this is indicated by a changing tone in earphones, or a needle moving on an indicator. Usually the device gives some indication of distance; the closer the metal is, the higher the tone in the earphone or the higher the needle goes. Another common type are stationary “walk through” metal detectors used for security screening at access points in prisons, courthouses, and airports to detect concealed metal weapons on a person’s body.
Metal detectors are used in De-mining (the detection of land mines), the detection of weapons such as knives and guns (especially in airport)geophysical prospecting, archaeology and treasure hunting. It is also used to detect foreign bodies in food, and in the construction industry to detect steel reinforcing bars in concrete and pipes and wires buried in walls and floors.