Metal detectors apparently date back to the
shooting of US President James A. Garfield
in July 1881. One of the bullets
aimed at the President lodged inside his body and couldn't be found.
Telephone pioneer Alexander Graham Bell promptly cobbled together an
electromagnetic metal-locating device called an
induction balance, based on an earlier
invention by German physicist Heinrich Wilhelm Dove. Although the
bullet wasn't found and the President later died, Bell's device did work
correctly, and many people credit it as the very first electromagnetic
metal detectors were invented by German-born electronics engineer
(which he also spelled "Fisher") while living in the United States, and
he applied for a patent on the idea in January 1933. He called his
invention the Metalloscope—a "method and means for indicating the
presence of buried metals such as ore, pipes, or the like". The
same year, he founded Fisher Research Laboratory, which remains a
leading manufacturer of metal detectors to this day. Dr Charles L.
Garrett, founder of Garrett Electronics, pioneered modern, electronic
metal detectors in the early 1970s. After working for NASA on the
Apollo moon-landing program, Garrett turned his attention to his
hobby—amateur treasure hunting—and his company revolutionized the field
with a series of innovations, including the first computerized metal
detector featuring digital signal processing, patented in 1987.