ever since jessica’s law (the lunsford act) states are required to track sex offenders once they’re released from prison. pro-tech makes the tracking device that is used in florida, shown above. the unit consists of an ankle bracelet with tamper sensing (patent 5,959,533 ” Tamper detection for body worn transmitter “) and a GPS tracking unit (patent 5,731,757 “Portable tracking apparatus for continuous position determination of criminal offenders and victims”) which has to be carried or worn near the ankle bracelet at all times. the system works mainly through GPS, but also contains accelerometers to determine position in case of lost signal from satellites. in addition both versions have a text display used to communicate with the agency and to issue warnings when the offender approaches a forbidden zone.