A brief from

Sept 2016

Use of Electronic Offender-Tracking
Devices Expands Sharply
Number of monitored individuals more than doubled in 10 years

Overview
The number of accused and convicted criminal offenders in the United States who are monitored with ankle
bracelets and other electronic tracking devices rose nearly 140 percent over 10 years, according to a survey
conducted in December 2015 by The Pew Charitable Trusts. More than 125,000 people were supervised with the
devices in 2015, up from 53,000 in 2005. (See Figure 1.)
All 50 states, the District of Columbia, and the federal government use electronic devices to monitor the
movements and activities of pretrial defendants or convicted offenders on probation or parole. The survey
counted the number of active GPS and radio-frequency (RF) units reported by the companies that manufacture
and operate them, providing the most complete picture to date of the prevalence of these technologies in the
nation’s criminal justice system.

Figure 1

Number of Active Electronic Offender-Tracking Devices Rose
Nearly 140%
Manufacturers report steady increase between 2005 and 2015
Number of total offender
tracking devices

140,000
120,000
100,000
80,000
60,000
40,000
20,000
0

2005

2006

2007

2008

2009

2010

2011

2012

2013

2014

2015

Note: The survey counted active GPS and radio frequency devices, except those used in immigration-related cases, every Oct. 31 in
the years studied. The count does not include information from manufacturers that went out of business or were acquired by other
companies between 2005 and 2015, so the actual numbers for each year may be higher than reported.
© 2016 The Pew Charitable Trusts

How electronic tracking works
Correctional authorities use ankle bracelets and other electronic tracking devices to increase compliance with
the conditions of pretrial release, probation, or parole among accused and convicted offenders residing in the
community. Although some electronic monitoring technology is intended to manage individuals’ behavior—
automobile ignition interlock devices, for example, can prevent those convicted of driving under the influence
from starting a car when intoxicated—tracking devices are used to monitor the movements or location of those
being supervised. The two dominant forms of tracking devices use GPS and RF technology.
•• GPS systems can continuously track offenders in real time, identifying their movements and whereabouts
by transmitting location information to monitoring centers and triangulating signals from satellites and
cellular towers.1 The devices are typically ankle bracelets worn by those whose movements are restricted by
court or parole board orders; however, some jurisdictions have replaced ankle bracelets with smartphones
equipped with GPS tracking capabilities.2 Convicted sex offenders, for example, may be barred from schools or
playgrounds, while those convicted of domestic violence crimes are commonly prohibited from approaching
their victims’ homes or places of employment.3 When monitored offenders enter such exclusion zones, GPS
devices alert supervising agencies, which can then take action.
•• RF devices monitor offenders’ presence in or absence from a fixed location. They are most commonly used to
supervise those on house arrest or confinement and to enforce curfews by monitoring an offender’s presence
either continuously or during specified times.4 RF systems consist of battery-powered transmitters, typically
worn around ankles or wrists, and home-based receivers that can verify whether offenders are within a certain
distance and alert monitoring centers of violations, allowing correctional authorities to take action.5

A new approach to measuring use of electronic
tracking devices
Establishing the exact number of offenders under electronic supervision is difficult, given the decentralized nature
of the criminal justice system. Earlier approximations have varied widely. For example, one study estimated that
more than 90,000 GPS units were in use nationwide in 2009,6 while the federal Bureau of Justice Statistics
reported that the figure was about 25,000 the same year.7 Both studies, however, were incomplete. The former
did not include a detailed methodology and did not indicate whether it counted only active monitoring devices
or inactive ones as well; the latter did not count defendants on pretrial release and relied on the voluntary
participation of state and local court and supervision agencies, many of which did not submit information.8
To provide a more up-to-date and comprehensive picture, Pew developed a survey of the 11 companies known
to manufacture, sell, or operate GPS and RF devices in the United States, including U.S. territories. Seven of the
largest companies responded, representing an estimated 96 percent of the market.9
Pew designed the survey to capture data on all active electronic tracking devices nationwide, including those
monitoring pretrial defendants or convicted offenders under federal, state, or local jurisdiction. The survey
excluded devices used in immigration cases because those offenses are generally considered civil in nature and
Pew sought instead to measure electronic tracking in the criminal justice system.10
To encourage greater participation, the survey granted confidentiality to all responding firms. To avoid doublecounting people who may have been tracked electronically at multiple points in one year, it asked companies to
count the number of devices in use on a single day—Oct. 31—from 2005 through 2015.11

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The survey uses the number of active devices as a proxy for individuals. Manufacturers do not have access to
information about the accused and convicted offenders supervised by their products.

GPS drove the increase in electronic tracking
The number of accused and convicted criminal offenders monitored with electronic tracking devices in the
United States increased 140 percent between 2005 and 2015, from approximately 53,000 to more than 125,000.
Extrapolating from the 96 percent market share of the companies that participated in the survey, the 2015 total
probably exceeded 131,000.
The survey also shows that a sharp increase in the use of GPS technology accounted for all of the 10-year growth
in electronic tracking, more than offsetting a decline in the use of RF devices. In 2015, manufacturers reported
that about 88,000 GPS units were being used for supervision of accused and convicted offenders, a thirtyfold
increase from the roughly 2,900 reported a decade earlier. By contrast, the number of active RF units fell 25
percent, from more than 50,000 to below 38,000. (See Figure 2.) These findings are consistent with published
studies that suggest RF devices are giving way to technology that can track offenders in real time.12
Despite the substantial growth of electronic tracking during the study period, it remains relatively rare in the
context of the U.S. corrections system. Nationally, nearly 7 million people were in prison or jail or on probation or
parole at the end of 2014, but individuals tracked using electronic devices in 2015 represented less than 2 percent
of that total.13 Although some research suggests that electronic monitoring can help reduce reoffending rates, the
expanded use of these technologies has occurred largely in the absence of data demonstrating their effectiveness
for various types of offenders at different stages of the criminal justice process.14

Figure 2

GPS Is Leading Electronic Offender-Tracking Technology
Number of active RF units fell 25%, 2005-15
Number of offender tracking
devices broken out by type

100,000
90,000
80,000
70,000
60,000

88,172

RF

50,132

50,000
40,000
30,000
20,000
10,000
0

37,706

GPS

2,897
2005

2006

2007

2008

2009

2010

2011

2012

2013

2014

2015

Note: The survey counts active GPS and RF devices on Oct. 31 of each year, excluding those used in immigration-related cases. It
does not include information from manufacturers that went out of business or were acquired by other companies between 2005
and 2015, so the actual numbers for each year may be higher than reported.
© 2016 The Pew Charitable Trusts

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Conclusion
Pew’s survey of electronic tracking devices provides the first valid, comprehensive count of the number of
accused and convicted criminal offenders monitored with GPS and RF technologies in the United States. More
than 125,000 people were tracked with the devices on a single day in 2015, up nearly 140 percent from the
53,000 reported on the same day in 2005. A sharp increase in the use of GPS technology accounted for all of
the growth, more than offsetting a 25 percent decline in the use of RF systems. Despite the overall expansion
of electronic tracking, however, the technology remains relatively rare in U.S. corrections, and additional growth
should be guided by rigorous research.

Acknowledgments
This brief was prepared for Pew by public safety performance project staff members Stephanie Fahy, Adam
Gelb, John Gramlich, and Phil Stevenson. This work was funded in part by The Pew Charitable Trusts with
additional support from the Laura and John Arnold Foundation. Editorial assistance was provided by Carol
Hutchinson, Jennifer V. Doctors, Bernard Ohanian, and Liz Visser. The project team thanks Kelly Hoffman
and Jennifer Peltak for production, design, and web support.

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Endnotes
1	

Tracy M.L. Brown, Steven A. McCabe, and Charles Wellford, Global Positioning System (GPS) Technology for Community Supervision: Lessons
Learned (August 2007), 1-1, http://www.in.gov/idoc/files/B_M_W_2007_GPS1.pdf.

2	 This survey did not include manufacturers of smartphone technologies that were not tethered to the offender under supervision because
those systems provide no assurance that the location of the phone correlates with the offender’s location.
3	

Matthew DeMichele and Brian Payne, Offender Supervision With Electronic Technology: Community Corrections Resource (2009), 33, https://
www.appa-net.org/eweb/docs/APPA/pubs/OSET_2.pdf.

4	 Ibid.
5	 Dennis Doffing, “BLU+ RF Monitoring,” The Journal of Offender Monitoring 25, no. 2 (June 2014), 19–21, http://www.utterbacksutterings.
com/wp-content/uploads/2014/06/JOM-2502-19-21-Doffing-STOP-Reprint.pdf.
6	 DeMichele and Payne, Offender Supervision, Table 1a. The authors attribute the estimate to Peggy Conway, former editor of The Journal of
Offender Monitoring.
7	 Bureau of Justice Statistics, Probation and Parole in the United States, 2009 (December 2010), Appendix Tables 11 and 22,
http://www.bjs.gov/content/pub/pdf/ppus09.pdf. Total includes offenders on probation and parole.
8	 DeMichele and Payne, Offender Supervision; and Bureau of Justice Statistics, Probation and Parole.
9	 To determine the market share captured by the survey, Pew consulted George Drake, an expert on offender-tracking technology,
who estimated that the four manufacturers that did not participate each accounted for less than 1 percent of the total number of
devices in use.
10	 One of the participating manufacturers had a contract with the Department of Homeland Security’s Immigration and Customs
Enforcement division (ICE) to provide monitoring for individuals involved in immigration proceedings. That manufacturer received a
separate survey with instructions to exclude numbers for individuals monitored for immigration-related proceedings or violations,
or any numbers associated with its ICE contract.
11	 Pew selected Oct. 31 to capture the most recent available data before distributing the survey to manufacturers.
12	 Doffing, “BLU+ RF Monitoring,” 19.
13	 Bureau of Justice Statistics, Correctional Populations in the United States, 2014 (December 2015), 1, http://www.bjs.gov/content/pub/pdf/
cpus14.pdf. Figure does not include pretrial defendants who are released from custody while awaiting trial.
14	 William Bales et al., A Quantitative and Qualitative Assessment of Electronic Monitoring (May 2010), https://www.ncjrs.gov/pdffiles1/nij/
grants/230530.pdf; Washington State Institute for Public Policy, “Electronic Monitoring (Probation)” (June 2016), http://www.wsipp.
wa.gov/BenefitCost/ProgramPdf/437/Electronic-monitoring-probation; and Marc Renzema and Evan Mayo-Wilson, “Can Electronic
Monitoring Reduce Crime for Moderate to High-Risk Offenders?” Journal of Experimental Criminology, 1, no. 2 (2005), 215–237,
http://link.springer.com/article/10.1007/s11292-005-1615-1#/page-1. Bales et al. found that electronic monitoring reduced the risk of
failure among medium- to high-risk offenders by 31 percent as measured by revocations for a new offense or a technical violation and
those resulting in a jail or prison sentence, and absconding; the Washington State Institute for Public Policy found that the benefits of
electronic monitoring for probationers exceeded the costs by nearly $27,000; and Renzema and Mayo-Wilson found that “applications
of electronic monitoring as a tool for reducing crime are not supported by existing data.”

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Contact: Kelly Hoffman, communications
Email: khoffman@pewtrusts.org
Project website: pewtrusts.org/publicsafety

The Pew Charitable Trusts is driven by the power of knowledge to solve today’s most challenging problems. Pew applies a rigorous, analytical
approach to improve public policy, inform the public, and invigorate civic life.