Alexander Graham Bell invented a kind of metal detector in 1881 in a to try and find the bullet in President James Garfield's body after he had been shot. The metal detector worked but it was confused between the bullet and a coiled bed-spring which he had been lying on. Gerhard Fischer made a better version in the 1920s but the detector got confused when someone was approaching ore-bearing rocks. He was given a patent in 1925.