Security metal detectors are usually used at buildings and locations that require visitors and employees to be checked for metallic objects including knives and weapons. They are highly sensitive and have been specifically designed to detect both large and small concealed metallic items containing ferrous metal. The detection indication can either be visual or auditory. You will often see them at airports, prisons, correctional facilities and law enforcement buildings and they are becoming far more common in schools, colleges, public buildings and sports stadiums.