When was the metal detector invented?

The first metal detector was invented in 1881 by Alexander Graham Bell. He attempted to use the device to locate a bullet in the chest of U.S. President James Garfield. Although the machine worked properly, Graham deemed it a failure because it was unable to locate the bullet.

Alexander Graham Bell did not realize that President Garfield was lying on a metal spring that confused his device. In 1925, Gerard Fischar invented a portable metal detector based on a system of radio-direction finding; it was sold commercially in 1931. During this time in Germany, H. Geffchen and H. Richter, invented the first walk-through metal detector.