Main content

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 waterproof, and shock-resistant transmitter affixed to the wrist or ankle of a participant 24 hours a day.  The ankle is the preferred location, and the wrist should be an option only for verified medical reason. The transmitter sends a constant radio signals back to the receiver when it is in a detectable range of the receiver. The officer is automatically notified when equipment is tampered with when in range of the receiver or when the participant enters/leaves a specific location (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 non-removable, waterproof, and shock-resistant GPS tracker is affixed to the ankle of a participant 24 hours a day. The participant is required to charge the GPS tracker at least daily or as directed. The participant’s location is detected by GPS satellites, cellular towers, and/or Wi-Fi.  GPS trackers receive satellite signals; they do not transmitter, nor do they require an unobstructed view of the sky.  GPS operations depend on an accurate time reference, which is provided by atomic clocks. Each GPS satellite transmits data that indicates its 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.

Virtual Monitoring Technology

Virtual monitoring using a smartphone mobile application requires participants to provide their whereabouts by using the devices locational services and identity technology (e.g., facial recognition, fingerprint, and/or password).   This technology is not included within the national contract and requires procurement of a non-competitive contract by an individual district.     

Restriction Levels in Location Monitoring

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


Curfew requires the participant 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.).

 A district’s local policy may establish specific criteria as a guide for officers to consider for determining curfew schedules.  The following local policy wording is provided as an example: “No curfew schedule may be given before 0600 or after 2100, unless it is employment/medical related.”

If curfew scheduling exceeds 16 hours outside of the residence (within a 24-hour period), court permission or supervisory approval should be sought and documented in the chronological record.

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 a component (e.g., curfew, home detention, home incarceration) restriction; 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 2023

Explore the other sections of the Location Monitoring Reference Guide.