This NIJ Guide provides the law enforcement and corrections community with information concerning the theory and limitations of hand-held (HH) and walk-through (WT) metal weapon detectors. It contains information to help the user better understand NIJ standards and specifications for HH and WT metal detectors. The Guide also includes general training instructions for metal detector operators and supervisors, information on where to obtain more detailed training, a brief discussion of safety topics, and a list of manufacturers.