Evaluating the performance of hand-held cellphone detectors in a prison setting.

Author:Russo, Joe
Position:NIJ Update

In response to the major and growing problem of contraband cellphones, (1) correctional administrators have increasingly turned to technological solutions to prevent contraband cellphones from entering facilities and to detect them. These solutions are marketed to administrators who are eager to address this critical issue. Unfortunately, products are often introduced into the correctional environment without rigorous, independent testing in an operational setting. To address this problem, the National Institute of Justice funded an evaluation (2) of one particular solution: hand-held cellphone detectors through the Corrections Technology Center of Excellence, which is part of the National Law Enforcement and Corrections Technology Center system. Three different types of detection devices were evaluated: radio frequency detection (RFD) devices, nonlinear junction detector (NLJD) devices and ferromagnetic detection (FMD) devices.

Each device that was tested employs a unique technical approach and, as a result, is better suited for some search applications than others. While direct comparison between devices is not appropriate, some key themes did emerge during testing. RFD devices performed extremely well at long ranges (70 to 125 feet), detecting each cellphone while producing no false alarms. Correctional officers who participated in the study preferred these devices for their utility during cellblock patrols. It should be noted, however, that RFD devices are effective only when the phone is actively making a call. NLJD and, to a much lesser degree, FMD devices were better suited for, and performed well in, the cell search scenarios due to their limited detection range (0 to 7 inches and 1 to 8 inches, respectively). Officers expressed concern, however, with false-alarm rates. The NLJD device produced false alarms at a rate of 28 percent for nonelectronics to 33 percent for authorized electronics; the FMD produced false alarms at a rate of 38 percent (authorized electronics) to 76 percent (nonelectronics). It should be noted that these high rates result, in part, from the presence of a variety of electronic devices and metals in a typical inmate cell. The evaluation produced evidence-based information that administrators can use to make cost-effective technology decisions based on their agencies' needs.

The Study

For the evaluation, researchers defined hand-held cellphone detector devices as ones that weigh less than 8 pounds, are powered...

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