How Location Monitoring Works

Available Location Monitoring Technology

The following technologies are currently available for LM use and are listed from the least to the most restrictive:

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.

This form of technology should be considered periodic spot-checking location sampling, not continuous 24/7 monitoring.

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 Mobile Applications (VM)

Virtual mobile application requires a mobile application (often referred to as an app) that is downloaded on the participant’s electronic device (e.g., smartphone, tablet) and uses biometric verification (i.e., facial comparison, fingerprint) and a password to verify the participant’s identity. The monitoring application requires the participant to report the participant’s location using the device’s GPS locational services to verify the participant’s presence at a location (e.g., residence, employment). This technology may require a mobile personal device capable of installing the application with an active data/service plan, front facing camera, and enabled locational services.

This form of technology should be considered periodic spot-checking location sampling, not continuous 24/7 monitoring.

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, VM is best suited to monitor lower risk, non-violent persons under supervision.

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 ankle of a participant 24 hours a day. 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. 

This form of technology is considered continuous 24/7 monitoring.

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 wrist or 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 transmit, 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. 

This form of technology is considered continuous 24/7 monitoring.

Under procedural guidance endorsed by the Criminal Law Committee, this data is closely monitored by the supervising officer. 

GPS technology 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. 

GPS wrist worn devices are best suited to monitor low-risk, nonviolent defendants, and persons under supervision or those with verified medical condition that does not allow for ankle-worn technologies as these devices do not offer the same features as a tradition ankle-worn device.

Component and Restriction Levels in Location Monitoring

The following program restrictions (i.e., components) are listed from the least to the most restrictive:

Curfew

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.).

It should be noted that case law determinations often limit an officer’s discretion related to restricting a participant’s liberties.  Any permanent changes (i.e., expansion, reduction) to the curfew requires court approval, as it changes the very nature of the restriction on the participant’s liberty.  However, the officer may situationally adjust the curfew time frame based on the participant's needs (e.g., employment medical reason, emergency) as a temporary adjustment, not a permanent change.

If ordered by the court, and consistent with case law, the officer may be authorized to establish the curfew time frame. 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 1200, 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;
• Essential leave; or
  • Note:a court-ordered pretrial condition that states "other activities as approved by the supervising officer" refers to essential leave
• Discretionary leave activities. 
  • For post-conviction home detention only

Home Incarceration

Home incarceration is the most restrictive component of the LM program.  It requires the participant to remain at the approved residence 24 hours a day, except for medical necessities, court appearances and other activities specifically approved by the court.  Participants who are supervised under a home incarceration component may not receive discretionary leave, essential leave, or leave for religious activities without the court’s approval.

Lack of Component in Location Monitoring

Stand-Alone Monitoring

Stand-alone monitoring refers to when the releasing authority orders use of LM technology without assigning an LM program component (i.e., curfew, home detention, home incarceration). The purpose of SAM is:
•    to use any type of LM technology — primarily GPS (ankle or wrist worn) or Virtual Mobile Applications — for supervision purposes; and
•    to monitor and enforce any other condition of supervision.

Last Updated: December 2024

Explore the other sections of the Location Monitoring Reference Guide.