A metal detector is a specialized gadget that is designed to locate metal objects. It is most commonly a handheld gadget with a headpiece or a pointer on a scale. It has a metal-sensitive electromagnetic probe on one end. This end is passed above the area you wish to scan, and it reacts with a sound or a pointer movement on a scale. The closeness of the metal object or metal ore is proportionate to the intensity of the sound or the pointer movement. The original idea was to create a magnetic field that would interact with metal objects lying beneath the ground. These objects would create their own field that would interfere with the one created by the metal detector. Measuring the changes in the created field of the probe would allow one to locate the object. This method evolved into an induction balance system, where two balanced coils lose their balance if a metal item is found nearby. Coil reaction to every metal is different, therefore such detectors are able to separate types of metal and metal ores detected, even filtering out the unnecessary ones. An alternative method is called pulse induction. A very strong but short impulse magnetizes the ground. If no metal is detected, the field created by the signal will gradually disappear, however, if there is a metal object underneath the ground, it will become magnetized and a field will take more time to disperse. This method is highly effective at locating small objects.
Application fields of such devices are numerous, from archaeology and amateur treasure hunting to mineral and precious metal prospection and mine detection. Mounted metal detectors are installed in crowded public places like airports, concert halls, embassies, etc. to detect weapons and explosives and prevent possible attacks.