Bugün öğrendim ki: En eski metal dedektörlerinden biri, telefonun mucidi Alexander Graham Bell tarafından Başkan James Garfield'ın Sandığı'na saplanan bir mermiyi bulmak için geliştirildi. Garfield'ın yattığı yatağın metal yaylarının müdahalesi nedeniyle onu bulma girişimi başarısız oldu.
Electronic instrument which detects the presence of metal nearby [![](//upload.wikimedia.org/wikipedia/commons/thumb/e/e2/B020311e_- _PFC_Generett_and_SGT_Rutledge_probe_in_yard_of_house.png/170px-B020311e_Generett_and_PFC) /File:B020311e_- _PFC_Generett_and_SGT_Rutledge_probe_in_yard_of_house.png) US Army soldiers use a metal detector A **metal detector** is an [instrument](/wiki/Electronic_instrumentation "Electronic instrumentation") that detects the presence of [metal](/wiki) Metal "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. 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 (see § Security screening below) used at access points in [prisons](/wiki/Prison