Companies interested in using x-ray systems and metal detectors as part of their protection arrays must understand both specific site considerations, the features commonly available on the market, and personnel selection and training. The selection process must include a threat profile, analysis of traffic flow patterns, and the likely location of the equipment. The features to look for, and to query manufacturers about, include: high immunity to interference, complete and uniform detection, good discrimination of objects, sensitivity to different metals, and the use of high-quality electronic components with low power consumption. Personnel who will operate the equipment must be properly trained and tested regularly, and each equipment station must be staffed with sufficient personnel. A walk-through metal detector and x-ray machine requires a four-person team: two persons to operate the machines, a security officer to conduct inspections with a hand-held metal detector, and a security officer to conduct physical bag inspections.