Industrial metal detectors indicate the presence of metal in nonconductive materials such as textiles, rubber, oils or liquids, plastics, powders, wood products, ceramics and glasses, and concrete. They are used to determine cleanliness or verify the absence of tramp metal in continuous or bulk products, as well as recycled materials. Applications include the detection of metal chips in pharmaceutical powders or preparations, nails or staples in wood, metal caps in crushed glass, and needles in fabric sheets. Industrial metal detectors are also used to verify the presence and location of metal such as buried electrical lines, piping behind walls, or reinforcing metal rebar in concrete. Airport metal detectors are used to detect guns, knifes, bombs, and other weapons. Industrial metal detectors for security applications can also be used to detect metallic items that an individual is trying to smuggle into or out of a secure facility.