Security metal detectors are designed to detect metal objects such as guns, knives and tools. If you have ever been through a metal detector arch, maybe at an airport or when entering certain public buildings, you will recall that you are asked to place all metal objects in a separate tray.
Metal detectors are those equipment's that are designed specifically to detect hidden metals. it can be used to detect metals that lie deep in the ground or water or otherwise in security matters to detect metals hidden by someone.