If one thing irks Thomas Heape, it's the sight of an 18-wheeler sitting idle under the big oak trees outside his office in Lakeland, Fla. Heape, 48, owns a 250-employee ServiceMaster janitorial franchise and sees far too many trucks parked under the trees at midday, an indication drivers are taking an afternoon nap on the job. ''That's just not right,'' he says. It might not be right but, at least until recently, employers couldn't do much to monitor such behavior.

That changed last year when a salesman showed up at Heape's office and offered him nine black boxes to install in his fleet of service vehicles - boxes that use the satellite-based Global Positioning System to chart a vehicle's each and every move. For $13,000, Heape was able to re-create his drivers' routes on a computer. The results were eye-opening. ''One guy stopped off at Wal-Mart for an hour and a half while on the job to go shopping,'' Heape recalls. This much was clear: There would be no more pit stops by workers at this ServiceMaster franchise.

But his action raises questions. While what Heape did as an employer was legal, ''the question becomes whether doing such a thing poisons your relationships with employees to the point that it ends up producing no benefit,'' says Barry Steinhardt, associate director of the American Civil Liberties Union.

In Heape's case, the GPS devices have helped improve efficiency. Now that employees are more mindful of how they perform on the open roads, fuel costs have decreased by 20 percent and overtime has plummeted by 70 percent. But has employee morale also sunk to new lows? Apparently not. ''At first I thought it was cracking down on my rights,'' says Jim Dmytryszyn, a project crew member. ''But I have nothing to hide, so I don't worry about it and have gotten used to it.''

GPS devices are being welcomed by business owners who want to squeeze every last ounce of efficiency out of their employees. But similar high-tech applications are also turning up in everything from rental cars to private vehicles, and one of the justifications being given for them is public safety. Still, some cases have raised questions about the potential to abuse the technology. Last summer, a New Haven, Conn., resident had $450 automatically deducted from his bank account for speeding in a GPS-equipped rental car.

Such uses of GPS tracking devices, in addition to other technologies such as red light cameras, have caused some to worry that their freedom behind the wheel is being threatened.

It's a big concern, especially to Americans who see their car as one of their last havens of privacy in a wired world. Some privacy advocates warn we are getting dangerously close to having an unwanted guest permanently in the passenger seat: Big Brother. ''All of George Orwell's worst nightmares are now technologically possible,'' Steinhardt warns.

If you're worried we might be moving closer to Oceania, the European/American mega-state in Orwell's novel ''1984,'' the main question becomes apparent: What are our rights behind the wheel, and how do they relate to our need for public safety?

As anyone who has lined up at an airport in recent months can attest, we are now more willing to allow for longer lines and more invasive searches to ensure air safety. With road accidents killing 42,000 in the United States last year, some argue that any technology that could improve safety while only slightly invading privacy may be worth considering.

''There is room to compromise,'' says Amitai Etzioni, a Georgetown University professor and author of a book on the limits of privacy. ''If there is a minor intrusion of privacy and a major gain on public safety, then that is a good bargain in my opinion.''

Red light cameras: Sign of things to come?

The delicate balance between privacy and safety has been highlighted by concern about red light cameras, devices that 60 US cities have installed to automatically photograph and ticket cars that speed through red lights.

A few days after an incident, a ticket arrives in the mail, complete with glossy photographic evidence of the infraction. Everyone agrees red light running is a serious problem. (It has been estimated to cause 260,000 accidents and 800 deaths a year.) But there is disagreement about whether red light cameras are the best way to improve intersection safety, even though one study showed cameras reduced red light running by 42 percent.

Some critics suggest the cameras aren't deterring accidents and are exacerbating the problem, because drivers are causing rear-end collisions in their abrupt attempts to stop and avoid expensive tickets. In San Diego, running a red light results in a $271 fine, levied on 2,500 to 5,000 drivers a month.

Civil liberties advocates worry about whether drivers' privacy is invaded by a camera capturing their license plate. Proponents of the cameras insist that a picture is only taken if a violation occurs and, regardless, people's license plates are already shown in public, wiping out any claims to the Fourth Amendment right to an expectation of privacy.

''I don't understand why people are upset about a camera taking a picture of their car when they violate the law,'' explains Judith Lee Stone, president of the Advocates for Highway and Auto Safety. ''Bank robbers have their pictures taken on security cameras. Is there anything wrong with that?''

Still, even Stone says red light cameras should only capture a car's license plate, not the driver at the wheel. Although most states only require a city to capture the license plate, California and Arizona require that the driver's face also be recorded. ''We've been trying very hard to get those states to change their laws so the owner of the car is liable regardless of who is driving, just like a parking ticket,'' explains Stone.

Most red light cameras rely on still photograph, but video-based systems are becoming more prevalent.

Nestor's Crossing Guard, a system installed in cities such as Irvine and Long Beach, Calif., and Falls Church, Va., creates a video file of a violator running the red light. The video is then reviewed by a police officer who looks at the context of the violation. If the ticket is contested, alleged offenders are asked to view the video segment at the police station. Before long, the Internet will be a part of the process. ''Soon we will be able to let violators view their red light infraction video over the Internet with a PIN number,'' says Nestor Traffic Systems' chief executive, David Fox.

Telematics: Your car gets wired

The Internet is already playing a role in telematics, which uses computers in concert with telecommunications systems. The field is expected to grow to the point where 11 million US cars will have some type of wireless data transmission capability by 2004. Services like GM's OnStar let users do everything from check e-mail to get directions, all from the driver's seat.

This is accomplished by combining cellular phone technology with a high-tech GPS chip. Like the technology installed in Heape's ServiceMaster fleet, GPS allows a car to communicate with an array of 24 satellites that orbit 11,000 nautical miles above the earth. The result is the ability to determine the position of a vehicle to within 100 feet. GPS has its benefits: When activated, OnStar can automatically alert authorities to a car's location when an airbag deploys, particularly important if drivers are knocked unconscious in a crash. But GPS also raises privacy concerns for skittish consumers worried that their every position might be monitored by others.

Concerns about tracking are apt to get even more intense this year as Wingcast, a joint venture between Ford and Qualcomm, introduces its service into 2003 model year Ford and Nissan cars. Wingcast plans to offer a feature called GeoSensing that will allow a car to automatically notify its owner via e-mail or phone when it leaves a certain predefined area.

''GeoSensing is like drawing a circle around the car and having the system notify you when the car goes out of that circle,'' explains Harel Kodesh, the Wingcast chief executive. Parents interested in making sure their children don't take the car too far away from home are liable to find an ally in GeoSensing. But the technology also suggests that real-time vehicle tracking is now a distinct possibility.

Both OnStar and Wingcast point out that these services are ''opt-in,'' that is, it's up to the owner whether to activate them. And they insist the position of a car is only known when a user contacts the call center or the company is ordered by a court to reveal the car's position. As Kodesh says: ''If you don't opt in for the service we have no way of finding you even if the authorities come to us. It would be like buying a cell phone and taking out the battery.''

Still, some privacy experts worry the pinpointing technology in cars could lead to a new form of telemarketing where your car's position becomes lucrative data.

''The fear is that telemarketers could use this information to dial you up on your cellphone as you pass a certain restaurant and say, `Why don't you come in and have a cup of coffee?''' says Mike Briggs, press secretary for Senator John Edwards, Democrat of North Carolina. Last July, Edwards introduced the Location Privacy Protection Act, a bill aimed at protecting consumers from having their GPS location revealed to third parties without authorization.

No matter what actions are taken, your car is quickly becoming part of the wired world. According to Forrester Research in Cambridge, telematics devices will be in 80 percent of new cars by 2006. With such pervasiveness expected in the near future, service providers, legislators, and privacy advocates agree this is the time to set up the appropriate checks and balances.