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

"These people probably should be in jail but the cost of incarceration can be as much as $30,000 or $40,000 a year. The GPS costs about $3,400 a year," he said.

"I think it's good on both sides. It is a device to protect the public. Although we can't guarantee anyone's safety, it provides an extra level of supervision on somebody. On the other side, for a defense attorney, it is in lieu of incarceration," said Lucci.

DOMESTIC VIOLENCE

The Massachusetts law was inspired in part by Cotter's death and other cases of repeated abuse in a country where authorities say more than 1,000 women are murdered each year by intimate partners. It alerts police whenever an offender enters a restricted zone such as near a woman's home or office.

"It's more than just slapping a GPS on a guy. You have to really have an intelligent coordinated approach to it and then it really can save lives," said Diane Rosenfeld, a professor at Harvard Law School who helped draft the Massachusetts law.

The Jeanne Geiger Crisis Center, a women's shelter which in 2006 began piloting the GPS program in Newburyport, a Massachusetts city north of Boston, has a high success rate -- none of the eight men fitted with GPS have violated protective orders while wearing the bracelets.

Kelly Dunne, associate director at the center, said Dorothy Cotter's murder highlighted several major problems. A judge, for example, released her husband without bail less than a week after he violated a restraining order and threatened to kill her. Five days later, he murdered her.

"As a result of that homicide, we now identify high-risk perpetrators as early as possible," she said. "In some cases the judge orders GPS," she said.

STRETCHED PRISONS

Authorities see it as an alternative to overflowing prisons in a country with the world's highest incarceration rate.