MADISON, WI - Hundreds of convicted sex offenders will have to wear a two-piece electronic tracking device for the rest of their lives under a new Wisconsin law.

Ankle bracelets and a pager-sized unit, often attached to a belt, will use Global Positioning System (GPS) technology to follow their every step. If they enter restricted areas, such as schools, officials will be alerted.

GPS programs will track 285 offenders the first year, beginning July 2007, and up to 400 by the second year, says Dan Leistikow, spokesman for Wisconsin Gov. Jim Doyle.

In May, Wisconsin joined a rapidly rising number of states using GPS to monitor convicted sex offenders. At least 23 states are doing so, according to a survey in February by the Pennsylvania Board of Probation and Parole. Others have since begun or expanded GPS programs.

"In the last several months, it's been exponential growth," says Steve Chapin, president of Pro-Tech, a Florida-based firm that provides GPS services to 27 statewide agencies. He says his business has doubled in the past three months.

As of January, 13 states had laws requiring or allowing GPS tracking, says the National Conference of State Legislatures.

Aside from Wisconsin, governors in at least six states (Arkansas, Georgia, Kansas, Virginia, Washington and Michigan) have signed such bills this year. New Hampshire Gov. John Lynch plans to do so soon. Similar bills are pending elsewhere.

"It's the law you can't vote against," says Chapin.

Several of the laws are named after Jessica Lunsford, a 9-year-old Florida girl who was kidnapped, raped and killed in February 2005. The man charged with killing her was a convicted sex offender who hadn't reported that he lived across the street from her family. After he fled, it took almost a month to find him.

Even states without specific GPS laws, including Minnesota and Texas, are testing the technology and expanding its use.

Congress may accelerate such efforts. The House and Senate have each passed sex offender bills this year that approve funding for GPS tracking. They need to craft a final bill.

More accurate technology

The surge in GPS use coincides with the technology's dramatic advancements. The devices have become smaller and more accurate, often pinpointing a person's position within 30 feet. They are more precise than older devices that use radio frequencies and detect only when the wearer leaves a certain area, such as home if under house arrest.

GPS units can be programmed to have "exclusion zones" where offenders are not allowed and "inclusion zones" where they should be.

States are spending $5 to $10 daily to track each sex offender. Some require offenders, unless indigent, to pay the tab. They can choose the costlier "active" tracking, which gives real-time reports, or "passive" monitoring, which sends one report daily that lists where the offender went that day.

States have tried both:

•California uses GPS to track 430 sex offenders and has funds to follow 2,500 offenders by 2009, says Elaine Jennings of the California Department of Corrections and Rehabilitation.

Since the program began in July 2005, 45 offenders have been arrested for violating parole and no new crimes have been committed, she says.

"It's an excellent supervision tool" but doesn't supplant human supervision, says Jennings.

•Massachusetts has issued eight arrest warrants for violations by the 192 high-risk offenders it has tracked since its "active" GPS program began in May 2005, says Paul Lucci, one of the state's deputy probation commissioners. The state has officers who constantly watch a computer screen recording offenders' whereabouts and who can respond immediately.

•Michigan finished three pilot programs in 2003 and plans this summer to begin tracking up to 1,000 sex offenders, says Steve Bock of the Michigan Department of Corrections' Electronic Monitoring Center.

Bock says the state will use "passive" monitoring, because "active" GPS is too labor-intensive. He says real-time tracking generates "a ton of messages" that necessitate a 24/7 response team. He says it's problematic if offenders are barred from many areas, because GPS allows only a certain number of exclusion zones.

"It can become a nightmare to enforce," Bock says.

Opposition to GPS tracking

Jake Goldenflame, 68, a convicted sex offender released 15 years ago, opposes lifetime GPS tracking. "If a man is so dangerous he needs it, he shouldn't be released," he says. Goldenflame says such monitoring may provide a "false sense of security," because it tells where the offender is, not what he's doing.

"It is not an effective way to prevent sexual assaults," says Richard Wright, a professor of criminal justice at Bridgewater State College. He says many serious sex offenders evade police by failing to register and others may re-offend regardless of tracking. He says no definitive study proves GPS deters crime.

Chapin says GPS reduces recidivism because offenders can't get away as easily. He says a December 2004 analysis by the Florida Department of Corrections found 3.8% of offenders tracked with GPS committed a new felony within two years compared to 7.7% of those supervised without it.

Offenders tracked by GPS were 90% less likely to abscond or re-offend than those not electronically monitored, says a February study by Florida State University of 75,661 offenders placed on home confinement. GPS did about as well as radio frequency, which costs four times less. "It's not a cost-free device," says Mark Carey, president of the American Probation and Parole Association. "It's an augmentation of what we do. It's not a replacement."