金属探测器利用电磁感应的原理，利用有交流电通过的线圈，产生迅速变化的磁场。这个磁场能在金属物体内部能感生涡电流。涡电流又会产生磁场，倒过来影响原来的磁场，引发探测器发出鸣声。

金属探测器不仅能探测军火及金属器械，还可以探测到硬币、锁匙及其他金属物品。因此在机场等场所会用来检查是否有妨害安全的金属物品，如刀械等被夹藏进入。

金属探测器现今也应用于食品，塑料等多个行业，检测产品中的金属，为提高产品纯度，防止杂物被混入。

A metal detector is an electronic instrument which detects the presence of metal nearby. Metal detectors are useful for finding metal inclusions hidden within objects, or metal objects buried underground. They often consist of a handheld unit with a sensor probe which can be swept over the ground or other objects. If the sensor comes near a piece of metal this is indicated by a changing tone in earphones, or a needle moving on an indicator. Usually the device gives some indication of distance; the closer the metal is, the higher the tone in the earphone or the higher the needle goes. Another common type are stationary "walk through" metal detectors used for security screening at access points in prisons, courthouses, and airports to detect concealed metal weapons on a person's body.