Go Ahead, Just Try to Disappear

As her daughter enjoyed a weekend road trip, Donna Butler sat back home 120 miles away at her personal computer and watched a blue dot tick slowly across the screen.

But not slowly enough.

"They were going 85 on the interstate where the speed limit is 70," said Butler, who interrupted 17-year-old Danielle's getaway to let her know, " 'I will personally come up there and drive you home.' "

It would have been easy to find her. Whenever Danielle is away from her central Florida home, her mobile phone uses a global positioning system to transmit her precise location, which her mother can track online.

Developed originally as a military tool, GPS is used widely by drivers, hikers and boaters to figure out where they are. A new generation of relatively cheap GPS-equipped devices can tell others too -- allowing people for the first time to keep constant tabs on their rebellious teens, wandering spouses or loafing employees.

That prospect comforts mothers like Butler, but it concerns some who see ever more powerful and invasive technology eroding a sense of personal privacy.

"If your supermarket offers you the chance to take a few cents off a loaf of bread in exchange for tracking every purchase you make with one of their cards, you do it," said Jonathan Zittrain, co-founder of the Berkman Center for Internet and Society at Harvard Law School.

"TiVo quietly makes note of your TV viewing habits. Will we be willing to carry a GPS locator so we can order a pizza with the push of a button and know it's on its way right to us?"

Although GPS was added to cellphones so that 911 emergency calls could be tracked, 15 million Nextel Communications Inc. subscribers can now buy the locator service for personal or business use. Next year the approximately 23 million Sprint Corp. wireless users will be able to sign up. It costs about $15 a month to turn on the service.

Among the first to sign up was James Kinney, to keep track of workers at his Kinney Construction Inc. in Orange. His employees are required to carry the phones during the workday.

Shortly after handing out the phones last year, office manager Kristy Collins was demonstrating the system for a supervisor.

"We looked at the map on the computer that showed all the little dots where a crew was working a job," Collins said. "But one dot was way over in another spot. The guy was at home instead of on the job."