Ankle monitor

An ankle monitor (also known as a tether, or ankle bracelet) is a homing device that individuals under house arrest or parole are required to wear. At timed intervals, the ankle monitor sends a radio frequency signal containing location and other information to a receiver. If an offender moves outside of an allowed range, the police will be notified. Ankle monitors are designed to be tamper-resistant and can alert authorities to removal attempts, such as cutting the conductive band causing a circuit break.

The most common configuration is a radio-frequency transmitter unit that sends a signal to a fixed location receiving unit in the offender's residence. The residence unit uses either a land line or a cellular network to relay information to a service center computer. If the offender is not at the residence at times stipulated, an alert message is sent to the service center, and then relayed to the supervising probation or parole officer. GPS units are similar in design, but the offender also carries a GPS cell phone unit that receives a signal from the ankle unit, or both functions may be combined into one ankle unit. Persons subject to a restraining order may also be subject to GPS monitoring.

Electronic monitoring was originally developed by a small group of researchers at Harvard University in the 1960s, headed by R. Kirkland Schwitzgebel and his twin brother, Robert Schwitzgebel (family name shortened to "Gable" in 1983). In 1983, Judge Jack Love in Albuquerque, New Mexico, inspired by a Spider-Man comic strip, initiated the first judicially sanctioned program using monitoring devices. These were produced by Michael T. Goss, a former Honeywell computer sales representative. Shortly thereafter, programs began in Florida using a cuff invented by Thomas Moody.

Within six years, at least 16 manufacturers were listed in the Journal of Offender Monitoring. In 2006, an estimated 130,000 units were deployed daily in the United States. They also gained popularity in the United Kingdom, but adoption in the rest of the EU was a little slower. A collection of early equipment and a written summary, with photographs, of the history of commercial devices in the United States is housed at the Archives of the History of American Psychology, University of Akron, Akron, Ohio, USA.

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