We can see that there are numerous types of metal detectors present. There are under water metal detectors, airport metal detectors and walk through devices and also handheld detectors. Most of these are used for security purposes and therefore are very common. People who are searching for objects or precious items under water especially in the deep sea make use of underwater metal detectors. They work underwater and under high pressure. As the visibility decreases as you go deep, it will be difficult to locate objects. However you can use underwater metal detectors to search for the desired item at any depth. Walkthrough and hand held metal detectors are used mainly for security purposes. They are constantly used in high security areas to ensure that no one is carrying any weapon or anything dangerous. If the device detects the presence of something metallic, it sets off the alarm and makes it easier for the guards to get hold of the metal object.