Electronic Monitoring FAQ

What are the technologies used for Electronic Monitoring in Corrections and Criminal Justice?

Electronic monitoring is the use of devices, protocols, and processes in the context of pretrial services, probation, truancy prevention, or other scenarios in order to determine compliance with rules and protocols established by a court or other agency. Agencies utilizing electronic monitoring range from local municipalities to the federal government. Electronic monitoring is used in a wide variety of applications including house arrest, drug treatment, immigration enforcement, truancy prevention, and other areas where the use of automated systems can increase the efficiency of an organization.

Electronic Monitoring, when utilized in the area of Corrections and Criminal Justice, can be divided into three primary categories based on the underlying technology used for a specific application. The three broad categories are GPS-based, RFID-based, and telephony-based systems. These systems may also utilize any combination of these technologies.

In many cases other technologies are incorporated within any of the three basic approaches. For example, an alcohol monitoring device might report via the telephony reporting system.

What are GPS-Based Monitoring Systems?

GPS-based systems rely on determination of position using the Global Positioning System satellite constellation, a network of satellites orbiting the Earth at fixed locations. These satellites broadcast signals which are used to determine the precise location of a receiver on the Earth. Due to the radio frequencies used for these transmissions the GPS signal may not be received inside buildings, underneath tree canopies, in areas surrounded by tall buildings, and other areas where the radio signal may be blocked or greatly attenuated, or which provides a limited view of the sky. A GPS-based monitoring system may track the movement of an individual, report that movement to a controlling authority such as a monitoring service or probation office, and may be used to determine whether the individual has complied with restrictions controlling where that individual may (or may not) travel.

The position resolution of GPS is dependent upon the technologies being employed however systems used for some applications are capable of centimeter accuracy. These systems use a reference datum, or point of known exact location, to increase their accuracy. This is impractical in most monitoring applications. For electronic monitoring systems the accuracy is typically on the order of tens of meters. Vertical resolution (elevation) is possible, but the accuracy is somewhat less than latitude and longitude calculation, and requires more satellite fixes for position determination than is required for latitude and longitude resolution. The satellite signal is in the GHz frequency spectrum and may be attenuated by water (e.g. rain) and building materials, and is blocked by metal. Thus a position reading may be impractical when the GPS device is within a building with a metal roof. The signal might also be blocked and position resolution might be prevented by covering the device with aluminum foil.

What is RFID?

RFID stands for Radio Frequency IDentification. An RFID system typically consists of a receiver and a transponder. The transponder is typically attached to the person whose location is being tracked. The receiver sends a signal to the transponder. The transponder sends a reply and the time it takes for the transponder to respond, or just the fact that a response was received, may be used to determine whether the individual is within range of the receiver. In some cases the actual distance or location relative to the receiver may be determined. In addition to proximity information an RFID system may be configured to supply additional information such as data from an alcohol monitoring device or other systems.

What are RFID-Based Monitoring Systems?

RFID monitoring systems are used to determine an individual's position using proximity or triangulation and use that information to determine an individual's compliance with court-ordered location sanctions. An RFID system typically consists of a reader and a transponder. The transponder is typically attached to the person whose location is being tracked. A reader interrogates the device by broadcasting a request to which the transponder replies. The reply usually contains unique identifying information for the device that is replying which allows for precise identification of the device. The time it takes for the transponder to respond or the fact that a response was received may be used to determine whether the individual is within range of the receiver and in some cases the actual distance from the receiver. In addition to this proximity information an RFID system may be configured to supply additional information such as data from an alcohol monitoring device or other systems.

In electronic monitoring applications the reader is often located in a fixed position in the subject's home and interrogates the tag worn by the client on an ankle bracelet or otherwise affixed to the subject. The receiver might utilize the telephone system to call a central location and deliver position or violation reports. The tag might contain sensors that detect drug or alcohol use and report that data when interrogated by the transponder. RFID systems are a good choice when a person needs to be monitored at a specific location with a high degree of certainty.

What are Telephony-Based Monitoring Systems?

Telephony-based monitoring systems use either wired or wireless telephone systems to monitor location of clients, transmit data pertaining to clients, or to interact with clients through interviews, voice print analysis, and other techniques. For example, a low risk offender might be interviewed on a regular basis to verify employment, residence, compliance with instructions, etc., and the results of the interviews reported to the controlling agency, thereby freeing officials to perform more critical tasks such as monitoring higher risk offenders. A person's voice print might be used in conjunction with caller ID or cellular phone location data to determine the compliance of a client with location restrictions. Telephony based electronic monitoring systems may be used to notify individuals of drug test reporting requirements, court dates, as well as for automated interviews to determine compliance with court-ordered sanctions, and for reporting changes in address, employment situation, and other information.

What is Self-Reporting?

Some cases under a court's jurisdiction are classified as low risk. The court may dictate monitoring protocols that call for an individual to report periodically where they are and their employment status, adherence to court instructions, arrests or other encounters with law enforcement, and other information. Rather than requiring the individual to contact their probation officer they may be required to call an automated system which collects the information specific to the case. This information may be forwarded to the controlling agency or alerts may be sent when a noncompliance event occurs.

What is an ankle bracelet?

An ankle bracelet (or ankle cuff) is a device that is affixed to an individual being monitored that reports data about the individual's location proximity to a fixed position, readings from devices that measure alcohol or other substances, or combinations thereof. Typically RFID technology is used to determine whether the head the device is in the proximity of a reader and the reader reports this to the central office by radio or telephone.

What is house arrest?

House arrest or home confinement is a court-ordered sanction requiring an individual to stay in their domicile where such protocol may or may not permit exceptions such as school attendance, physician or mental health visits, work, or other exceptions. Often this is used for those considered low to medium risk.

What is speech recognition?

Speech recognition is computer analysis of spoken words which determines what an individual says and may be used in a combination voice biometrics to determine the identity of an individual speech recognition.

What are Voice Biometrics?

Each person's speech has unique patterns which may be used to confirm the identity of an individual. Voice Biometrics is the use of these speech characteristics for identity analysis.

What is Alcohol Monitoring?

Alcohol monitoring is the use of alcohol sensor devices to determine alcohol usage by an individual. The sensor may attached to an ankle bracelet or other device which keeps the sensor in close proximity to the skin, or in some cases a device used to measure alcohol in an individual's breath may be used in order to determine whether the individual has complied with the restrictions concerning consumption of alcoholic beverages. An alcohol monitoring device may be used in an interlock to prevent an individual from starting an automobile when that individual has consumed alcohol. Alcohol monitoring is typically part of a total electronic monitoring package for an individual, particularly when that individual has a problem with alcohol or drugs.