Though Martha Stewart donned an electronic ankle bracelet during her house arrest, it's unlikely that GPS tracking devices will become a fashion statement any time soon. Still, the devices, used to track paroled criminals, are gaining in popularity: Twenty-three U.S. states use GPS tracking for convicted sex offenders, and some states, such as Florida, are using it as an inexpensive transition program for low-risk offenders, to make room in the state's already-crowded prisons for new admissions.

The most common way to track offenders is with a "passive" device (usually a bracelet worn on the wrist or ankle) that provides next-day reports on where the subject went throughout the previous day, allowing parole officers to ensure the offender didn't stray into any "exclusion zones" (schools or playgrounds in the case of sex offenders, for example). Real-time, or "active," tracking constantly transmits the subject's location (as long as the device can access a cellular network), and sends alerts to a parole officer's e-mail address or cell phone if his charge enters an exclusion zone.

Until recently, tracking technologies suffered from one major drawback: They didn't work indoors. But Todd Young, director of product and business development at Rosum Corp., thinks he has found a way around that. The Mountain View, Calif.-based company developed a technology that uses television signals to track the device, even when a satellite can't pick it up.

The refinement of the tracking technology comes not a moment too soon. As Florida is discovering, GPS tracking can provide both a deterrent to recidivism, and a way to garner support from communities that may otherwise be skittish about prisoners' early release, says Peggy Conway, editor of the Journal of Offender Monitoring. To avoid overcrowding at the state's facilities, Florida has 955 offenders using tracking devices, and 774 are active GPS systems. The state uses the devices for released sex offenders, drug offenders and low-risk inmates who could benefit from a structured transition program.

Tod Depp, program manager of testing and evaluation at the Rural Law Enforcement Technology Center in Hazard, Ky., which performed extensive tests on active GPS tracking devices for New Mexico's Corrections Department, says that some parole and probation officers are concerned about the added liability that comes with tracking capabilities. "These officers are not highly paid and may already have burdensome case loads," says Depp. "One officer who was testing tracking devices said, 'If my cell phone rings at 4 a.m. with a tracking alert, I'm not going to pick it up.'"

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