For ages, man has hammered against rock to obtain precious materials from the earth's surface. This can coal, ore, diamonds and other minerals but during that time, metal detectors were both crude and primitive. It is only by hitting the ground and listening to the sound that will determine if there was something underneath.
It was not until the 1930's that engineers were able to develop a system that works based on the radio frequency. This was better than using the hammer in the past but the device was quite heavy with a heavy battery pack carried on the person's back.
Further improvement with this machine happened during the second world war. Soldiers used this to clear an area of landmines so that troops can move forward. The metal detector became useful again when incidents of hijacking occurred in the 1970's, which prompted airports and other vital installations to come up with a way to deter such a threat.
Today, the security metal detector comes in all shapes and sizes. Security personnel can use a stationary machine where the person has to walk through to check for knives, bombs and concealed weapons. In places that this is not applicable, the hand held version can be used.
Users of the security metal detectors can increase the sensitivity of the machine. This means the alarm will even sound if the individual has a set of keys, a mobile phone or some coins in the pocket.
The person will just have to bring it out to show the one manning the gate before going any further.
But the metal detector is not only used for security. Hobbyists and archeologists also use this to either find buried treasure or artifacts. There are also different models available and the high tech versions can determine the size, weight and description of the object even before this has been excavated.
The difference in terms with those used by security and hobbyists is that those assigned at a certain posts do not need to use headphones. When something is detected, the people there will will immediately go request the person to empty the pockets and walk through the machine again to make sure there are no problems.
Should the alarm still sound, there could still be something on the person or there is a problem with the machine.
Metal detectors have evolved from simply searching for minerals to applications for military and civil use and this will continue until a better machine comes along to replace the old system.