GPS grows as a crime-fighting tool in U.S

The number of people in U.S. prisons has risen eight-fold since 1970 to 2.2 million people -- nearly a fourth of the world's total, according to the Sentencing Project, a research and advocacy group.

North Carolina's eastern Pitt County, a rural tobacco-growing region of 138,690 people, adopted the technology in late 2005 to relieve overcrowded jails by freeing more accused batterers on bond and tracking them with GPS before they go to trial. It was expanded last year to four more counties.

In a measure of success, police dispatchers receive fewer calls involving the same person when an offender wears a GPS bracelet. Pitt County's recidivism rate for domestic violence fell from 36 percent in 2004 to 14 percent this year, said Sgt. John Guard of local sheriff's domestic violence unit.

But once batterers finish the program and go off GPS, the rate shot back up to around 40 percent, he added.

"It may help in the short term pre-trial. But post-trial, it's not. That tells me there are other things we have to do to ensure the safety of the victims," he said.

There are other concerns. Los Angeles Superior Court Judge Michael Linfield warned a Harvard Law School panel in February that GPS may offer only a "high tech illusion of safety" that fails to do more to protect women than traditional restraining orders, according to the law school's newspaper, The Record.

"We don't ever say to anyone that this will save your life," said Barry Bryant, deputy director of the Governor's Crime Commission in North Carolina.

"It doesn't really guarantee much because the truth is it's real time. If someone has entered a zone where they shouldn't be, can you get there before they do something violent? I don't know. But it's an added measure of safety."

He said police, not the court, mostly determine who wears the surveillance bracelets in North Carolina -- a nuance that raises civil liberties concerns.

"This should be done by independent judicial officials, not by police officers whose job is to investigate, not to mete out justice," said Barry Steinhardt, head of the American Civil Liberties Union's technology program in Washington.