SNM monitors are an efficient and sensitive means of unobtrusively (without a body search) meeting the requirements of 10 CFR (Code of Federal Regulations) Part 73 or DOE Order 5632.4 (May 1986) that individuals exiting nuclear material access areas (MAAs) be searched for concealed SNM. The monitors sense radiation emitted by SNM, which is an excellent but otherwise imperceptible clue to the presence of the material. Because the monitors operate in a natural radiation environment and must detect small intensity increases as clues, the monitors must be well designed and maintained to operate without unnecessary nuisance alarms. This guide provides information on different types of monitors for searching pedestrians and vehicles. Each monitor has an inherent sensitivity at a particular nuisance alarm rate that must be low enough to maintain the monitor’credibility. Sensitivity and nuisance alarm rates are both governed by the alarm threshold so it is very important that corresponding values for both be known when measured, estimated, or specified values are discussed. Fitting SNM monitors into a facility physical protection plan must not only consider adequate sensitivity but also a sufficiently low nuisance alarm rate.1.1 This guide briefly describes the state-of-the-art of radiation monitors for detecting special nuclear material (SNM) (see 3.1.11) in order to establish the context in which to write performance standards for the monitors. This guide extracts information from technical documentation to provide information for selecting, calibrating, testing, and operating such radiation monitors when they are used for the control and protection of SNM. This guide of