It's 10 p.m. -- Do you know where your children are? How about your pet? Or your spouse who claims to be "working late"?

Global Positioning System technology, more commonly known as GPS, is making it easier than ever to find stolen cars or track down Fido when he gets lost.

But the system also can monitor people, a move privacy experts fear could go too far.

"The control of GPS tracking information will be a significant public policy issue several years from now," Phil Agre, an associate professor of information studies at UCLA and a member of the board of the Electronic Privacy Information Center. "Everyone should be aware of the dangers before the it becomes locked in."

So far, GPS has been an invaluable tool for tracking endangered salmon, monitoring train schedules and even drawing up maps. Companies such as Troy, Onstar and Microsoft have developed GPS systems for cars that send directions to drivers based on their locations. Some even call the owner when a car "thinks" it's been stolen.

In Pontiac, Michigan, non-violent prisoners wear GPS-based bracelets in lieu of serving time behind bars. Systems are also in the works to ensure Alzheimer's patients stay close to the hospital and children don't stray too far from home.

"Maybe these are benign uses, but where does it stop?" asked Agre.

Agre and other privacy experts worry about misuse of the information by groups ranging from insurance companies to the FBI.

Scary scenarios
Among the scenarios feared by privacy watchdogs:

Insurance companies could refuse to insure you, or charge you higher rates, unless you install a tracking system on your car. They could then tell if you drive over 55 or spend time in shady neighborhoods where your car has a greater chance of being stolen.

FBI and local police officials could have access to your whereabouts by simply logging onto a database attached to a cell phone, tollbooth or GPS tracker. New York transportation authorities have turned over records of its E-Z Pass toll, a wireless system that lets people drive through without stopping, to police during a criminal investigation. What if it turned the same information over to a local restaurant, so it knew you drove by it every day?

Private investigators could get their hands on geographic tracking data to trap a spouse suspected of straying. Gotcha! -- if toll bridge records showed you driving when you were supposed to be at work.

Follow the data trail
Privacy advocates fear agencies that aren't used to handling private information, such as transit authorities, will become the keepers of personal facts and figures that people don't necessarily want to be in the public domain.

But other privacy experts said such worries are simply alarmist. "A lot of the privacy stuff I think is a little overblown," International Data analyst Chris Christiansen said.

Currently, the systems are too expensive to be prevalent at the consumer level -- plus many of the cheaper consumer devices are hindered by heavy rain, trees and tall buildings, he said.

Originally developed to help the military track wayward sailors, GPS is made up of 24 satellites, each with a clock, positioned so that three are always above the horizon. Earthbound receivers can determine the position of a person, place or thing by measuring the amount of time it takes for a signal to arrive from three of the satellites.

Tracking people by GPS is not even prevalent enough for the ACLU -- known for jumping on a cause at the slightest sign of injustice -- to take a stand. Carrie Moss of the ACLU of Michigan -- which has closely watched her area's plans to monitor prisoners -- said her organization wouldn't object to tracking a shoplifter for a specific amount of time in lieu of jail time. But it would fight efforts to track people who'd been convicted of shoplifting once for the rest of their lives.

Matter of control
Kanwar Chadha, founder of GPS company SiRF Technology, said the issue comes down to who controls the information in a GPS system.

"GPS by itself only tells you where you are," said Chadha, whose company makes GPS-based chipsets that can be embedded in cell phones, automobile systems and handheld computers. "It's really when you combine GPS with some kind of wireless system that privacy becomes an issue."

For example, Chadha said users of SiRF's products must push a button on their GPS device if they want to transmit their whereabouts. Under this system, companies or organizations can't track users without their permission.

However, privacy concerns could arise under a model where control is shifted back to the network -- as it would be with systems used to monitor groups like Alzheimer's patients or children.

"Privacy is always an issue when you have a system that allows you track somebody," Chadha said.

Chadha predicts consumers will protect their own privacy, by refusing to deal with companies that threaten to violate it. Already, privacy groups have pressured Intel to back away from shipping chips that automatically identify a computer to a network.

For geographic tracking systems, Chadha said privacy isn't an issue, as long as users control the transmission of their own location information.

"But it's an issue if somebody else plants the device on you," Chadha said. "That's what I would call a misuse of the technology."

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