The metal detector is over a century old — and its story runs through a presidential assassination attempt, two world wars, and the transistor revolution.
The metal detector is over a century old — and its story runs through a presidential assassination attempt, two world wars, and the transistor revolution.
The idea is older than electronics. In the 1830s–40s, experimenters played with induction balances — arrangements of coils where a nearby piece of metal disturbed the balance and revealed itself. In 1881, Alexander Graham Bell built an induction-balance device to locate the bullet lodged in President James Garfield after his assassination attempt. It failed: the metal springs of Garfield's bed confused the detector. The bullet was never found that way, but Bell's two-coil design would evolve into the Double-D coil still used today.
Gerhard Fischer, working on radio direction-finding for aircraft navigation, noticed his equipment behaved strangely over ore-bearing rock. Reasoning that a radio beam distorted by metal could be turned into a detector, he applied for the first electronic metal-detector patent in 1925. (Fischer later founded Fisher Labs — one of the brands we track today.) An American businessman, Shirl Herr, had filed for a hand-held "Hidden-Metal Detector" a year earlier, in 1924; his machine reportedly located objects left by earlier Antarctic explorers.
The first truly practical detector was a wartime invention. Polish officer Józef Kosacki, stationed in Scotland, refined the design into a working mine detector; 500 units were shipped to Montgomery's forces for the Second Battle of El Alamein to clear German minefields. The units ran on vacuum tubes with separate battery packs — heavy, but they worked. Because it was a military secret, Kosacki's authorship stayed classified for over 50 years.
Transistors shrank everything. Charles Garrett pioneered the BFO (beat-frequency oscillator) machine — simple, affordable, and the technology that launched hobby detecting as a pastime. Companies sprang up across the US and Britain. In the 1970s, coil designers introduced the Double-D ("widescan") coil layout, and tunable induction systems gave machines their first real discrimination: the ability to tell iron from silver by phase response. Detectors learned to cancel out ground mineralization — the ancestor of today's ground-balance systems.
Microprocessors turned detectors into computers you swing: stored programs, notch filtering, target ID numbers, multi-frequency transmission. Wireless audio, Bluetooth, GPS find-logging, and smartphone apps followed. The physics hasn't changed since the 1830s — a coil, a field, eddy currents in metal — but a 2026 flagship processes the return signal in ways Fischer could never have imagined.
There's no single inventor. Early induction experiments date to the 1830s–40s, Alexander Graham Bell built a bullet-finder in 1881, and Gerhard Fischer received the first electronic metal-detector patent in 1925. The first practical field machine was Józef Kosacki's WWII mine detector.
Military and industrial work came first: locating unexploded ordnance after WWI, clearing minefields in WWII, and finding minerals. Hobby treasure hunting only took off in the 1960s–70s once transistor BFO machines made detectors affordable.
BFO (beat-frequency oscillator) — the 1960s technology Charles Garrett commercialized. It's obsolete for serious detecting, but VLF, pulse induction, and multi-frequency all descend from the same induction-balance principle. Our technology guide explains the modern three.
As tools, rarely — a 1970s machine is outclassed by a modern budget detector in depth, discrimination, and weight. As collectibles, early Garrett, White's, and Fisher units have a small collector market. For actual detecting, buy modern.
This is a condensed history drawn from public records. Dates and attributions follow the standard published accounts; the hobby's early commercial history is patchy, and some claims from that era are marketing as much as fact.