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How Location Monitoring Works

Available Location Monitoring Equipment

The following equipment is currently available for LM use:

Radio Frequency (RF)

Landline Unit or Receiver

This technology involves a receiver that requires an electrical power source as well as a telephone landline to transmit data. Persons under supervision using this technology wear a non-removable transmitter affixed to their ankle, which sends signals back to the receiver when it is in a detectable range of the receiver. The officer is automatically alerted by the receiver when the monitoring equipment is tampered with, or when the person under supervision deviates from an approved schedule or leaves a specific location, typically the residence. 

Cellular Unit or Receiver

This receiver has the same requirements and features as the landline receiver but transmits data via cellular signal; thus, no telephone landline is required.

RF technology remains the most effective monitoring technology to verify the presence of a person under supervision in the residence during specified hours. Under procedural guidance endorsed by the Committee on Criminal Law of the Judicial Conference of the United States (Criminal Law Committee), officers are required to respond to violations; however, locational data is only available for the location where the monitoring unit is placed. 

Global Position System (GPS)

A GPS tracker is affixed to the ankle of a person under supervision. The tracker receives satellite signals that transmit data to indicate the tracker location and current time. Under procedural guidance endorsed by the Criminal Law Committee, this data is closely monitored by the supervising officer. 

GPS equipment may be the preferred supervision tool when enhanced supervision is needed and the whereabouts of the person under supervision must be monitored when leaving the approved residence, or when a third-party risk has been identified. 

Voice Recognition (VR)

Computerized random or scheduled telephone calls are placed and received from a person under supervision’s approved location, typically the residence, to verify the person’s presence. This technology requires a telephone landline.

Under procedural guidance endorsed by the Criminal Law Committee, a violation does not require an immediate response, but officers are expected to investigate any violations within one business day. For these reasons, VR is best suited to monitor lower risk, non-violent persons under supervision.

Restriction Levels in Location Monitoring

The following LM restriction levels are listed from least to most restrictive:


Curfew requires the person under supervision to remain at an approved residence during set time periods of the day (e.g., between 8:00 p.m. and 6:00 a.m.).

Home Detention 

Home detention requires the person under supervision to remain at an approved residence at all times, except for the following scheduled absences that have been preapproved by an officer:

  • Employment;
  • Education;
  • Religious activities;
  • Treatment;
  • Attorney visits;
  • Court appearances;
  • Court-ordered obligations; or
  • Other activities as approved by the officer.

Home Incarceration

Home Incarceration requires 24-hours-a-day lockdown, except for medical necessities and court appearances or other activities specifically approved by the court.

Stand-Alone Monitoring

Stand-alone monitoring does not involve residential curfew restrictions; however, the person under supervision must comply with the location or travel restrictions as imposed by the court. Stand-alone monitoring should be used in conjunction with GPS technology.

Last Updated: March 2020

Explore the other sections of the Location Monitoring Reference Guide.