In 1881, Alexander Graham Bell invented the first metal detector. As President James Garfield lay dying of an assassin's bullet, Bell hurriedly invented a crude metal detector in an unsuccessful attempt to locate the fatal slug. Bell's metal detector was an electromagnetic device he called the induction balance.

Gerhard Fischar

In 1925, Gerhard Fischar invented a portable metal detector. Fischar's model was first sold commercially in 1931 and Fischar was behind the first large-scale production of metal detectors.

According to the experts at A&S Company: "In the late 1920's, Dr. Gerhard Fisher, the founder of Fisher Research Laboratory, was commissioned as a research engineer with the Federal Telegraph Co. and Western Air Express to develop airborne direction finding equipment. He was awarded some of the first patents issued in the field of airborne direction finding by means of radio. In the course of his work, he encountered some strange errors and once he solved these problems, he had the foresight to apply the solution to a completely unrelated field, that of metal and mineral detection."

Other Uses

Simply put, a metal detector is an electronic instrument which detects the presence of metal nearby. Metal detectors can help people find metal inclusions hidden within objects, or metal objects buried underground. Metal detectors often consist of a handheld unit with a sensor probe which the user can sweep over the ground or other objects. If the sensor comes near a piece of metal, the user will hear a tone, or see a needle move on an indicator. Usually, the device gives some indication of distance; the closer the metal is, the higher the tone or the higher the needle goes. Another common type is the stationary "walk through" metal detector which is used for security screening at access points in prisons, courthouses, and airports to detect concealed metal weapons on a person's body.

The simplest form of a metal detector consists of an oscillator producing an alternating current that passes through a coil producing an alternating magnetic field. If a piece of electrically conductive metal is close to the coil, eddy currents will be induced in the metal, and this produces a magnetic field of its own. If another coil is used to measure the magnetic field (acting as a magnetometer), the change in the magnetic field due to the metallic object can be detected.

The first industrial metal detectors were developed in the 1960s and were used extensively for mineral prospecting and other industrial applications. Uses include de-mining (the detection of land mines), the detection of weapons such as knives and guns (especially in airport security), geophysical prospecting, archaeology, and treasure hunting. Metal detectors are also used to detect foreign bodies in food as well as in the construction industry to detect steel reinforcing bars in concrete and pipes plus wires buried in walls or floors.