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GPS monitoring uses satellites to calculate a person's physical position. The person wears a tamper-resistant bracelet — typically worn around the ankle — that receives transmissions from the satellites and calculates their location. In "passive" monitoring systems, this information is stored and transmitted at appointed times to a monitoring station. In "active" systems, information on the individual's location transmits to a monitoring station in near real time, allowing the station to alert officers immediately when a violation occurs. Both systems allow exclusion zones (such as schools or other places where children congregate) or inclusion zones (such as a workplace) and provide information on when and where an individual has been throughout the day.
In California, individuals designated as high-risk are placed on actively GPS-monitored caseloads, while non-high-risk persons are on passively GPS-monitored caseloads. However, in the state, information in both caseload types is received at near-real-time intervals. The difference is that information in the active system is reviewed more frequently than information in the passive system. Vendor-operated monitoring centers track this information and email daily reports to parole agents that detail all of the activity recorded by the GPS device. The centers also send an immediate alert notification to agents via text message whenever the GPS device records an inclusion/exclusion zone violation, tampering with the strap, a low battery, a cell communication gap or no GPS communication.
About This Article
This article appeared in NIJ Journal Issue 271, February 2013, as a sidebar to the article Sex Offenders Monitored by GPS Found to Commit Fewer Crimes by Philip Bulman.