Metal detectors work by sending and receiving electromagnetic fields. A search coil sends an electromagnetic field into the ground. That field energizes any metal object it contacts, then the object sends an electromagnetic field back up. Once that field reaches the search coil, it is detected and an alert sounds on the metal detector.
Metal detectors have a variety of uses. They have been used for archaeology since 1958. Many people use metal detectors as a hobby, looking for coins or valuable items buried underground. There are even metal detecting clubs in which hobbyists meet and socialize.
Metal detectors are also used for security purposes. Soldiers use metal detectors to search for land mines, and metal detectors are used in certain areas, such as airports, to check people for concealed weapons. They are also used to inspect goods, such as food and clothes, for metal fragments before consumers can purchase them.
The first metal detectors were created in the late 19th century. Gerhard Fisher came up with the idea of using a search coil resonating at a radio frequency, and in 1925 he obtained the first patent for a metal detector. Smaller metal detectors started being manufactured in the 1950s with the development of the transistor.