About the size of a carpenter's tape measure, it's often stashed under your dashboard or seat and linked to the deployment of your airbag. But growing privacy concerns are making these obscure little "black boxes" suddenly controversial.

"Ninety percent of people don't even know this thing is even in their car," said Bob Smith, executive director of the Society of Collision Repair Specialists for Missouri and Kansas, which represents crash reconstruction investigators.

It's estimated 70 percent or more of all new cars already are equipped with what are called EDRs, or event data recorders. They can record everything that happened before and after an accident - including car speed, engine revolutions, braking and seat belt use.

While the device is constantly monitoring the car's operation, it can record the information only in the five to 10 seconds before and after it senses a crash serious enough to deploy an airbag.

Crash investigators, insurers, police and government researchers say such information is invaluable in learning how to make safer cars and save lives. But privacy advocates fear a darker side in which insurers, police and researchers gain unbridled access to data that can be used to incriminate consumers.

Such privacy concerns are certain to heighten later this year when the National Highway Traffic Safety Administration issues a new rule requiring car makers to standardize black-box technology so data are recorded and stored the same way and are easier for researchers to harvest and compare.

Right now, both General Motors and Ford, the two domestic car makers who account for the greatest use of the data recorders and who have been the most open about their use in law enforcement situations, employ competing technologies.

The proposed rule falls short of mandating black boxes in all cars but will require all automakers to tell consumers that they exist. Today only some owner's manuals alert car owners there is a black box on board.

So far, only about a dozen states have addressed black boxes, mainly with laws to ensure consumers' ownership rights to the data. And there has been little federal discussion.

Meanwhile, some insurance groups want to ease access to the data to set rates - rewarding some drivers and penalizing others - and also to prove claims fraud in the same way DNA is used to prove paternity.

Possible future applications for black boxes are even more far-reaching. Technology already exists that would allow more information to be recorded about a driver's acceleration and steering. It also could record the time and date of an accident and, using cell phone technology, relay life-saving information to emergency crews.

"A lot of people are afraid of this technology, but in the future it will bring a safer car," said Steve McKinzie, owner of McKinzie & Associates, an Olathe, Kan., crash reconstruction and investigation company.

Even so, information that can be used to save lives might also one day be remotely accessed by police monitoring your car's speed by satellite as you hurry home from work. The devices could make traffic radar guns obsolete.

"Keep in mind that driving a car in Missouri is a privilege and not a right," Terman said. "The sooner we can get all cars to have this information on board, the safer we will be. This will be the policeman under the hood, so to speak."

But such potential applications, privacy advocates say, raise questions about who really owns the data and the privacy expectations of the driving public.

"Like most things it's a mixed bag," said Jim Harper, director of information policy studies at the Cato Institute and editor of Privacilla.org, a Web site devoted to privacy issues.

"There are benefits to manufacturers to improve safety and to law enforcement to know what happens before a crash," he noted. "But it can deprive a consumer of the right to choose. In what other area of life are we required to collect data that incriminates us?"

These privacy issues could hardly have been envisioned when the boxes - actually silver and less sophisticated than the well-known black boxes on airplanes - were first installed in cars in the late 1990s to monitor air bags.

Automakers came up with computer technology that could better predict a serious accident and control deployment of the airbag. Sensors trigger a mechanism to adjust the seat belts to limit the impact of the bags.

"The biggest potential from the standpoint of safety researchers is that we would be able to get much more extensive and potentially more accurate information of what happens in real crashes," said Russ Rader, spokesman for the Insurance Institute for Highway Safety, which studies crashes.

Mindful of the value to better engineering, the auto industry has nevertheless publicly stated the data belong to a vehicle's owner. GM, for example, has a policy that it will not access the information or share it without consent of the car's owner, unless ordered to by a legal proceeding.

The Alliance of Automobile Manufacturers, which represents domestic and foreign automakers, has drafted model legislation for states to use in addressing privacy laws. Spokesman Eron Shosteck said that legislation makes clear the information "is the sole property of the vehicle owner."

The problem, however, is that consumers can give up the right of ownership when they sign an agreement to get insurance coverage - or if they get hit with a search warrant or court order.

In the absence of laws to the contrary, police contend that in instances mainly involving fatal accidents they have probable cause to download black boxes at the crash scene. If they impound the car, they will seek a search warrant.

"If we anticipate a felony prosecution we'll try to get the black box," said Sgt. G.Q. Billings, a Missouri Highway Patrol fatal collision reconstruction expert. "It has proven useful."

Cape Girardeau County Prosecutor Morley Swingle used a black box to prosecute a drunken-driving case two years ago in which two passengers died. Data from the black box showed Scott L. Bragg hit a culvert at 118 mph when his Pontiac Firebird became airborne and skimmed phone lines.

Although the defense argued the Highway Patrol downloaded the black box without a search warrant, the judge ruled there was probable cause. Bragg almost immediately pleaded guilty and was given a 21-year-sentence.

"It was pretty damning evidence," said Bragg's attorney, Steve Wilson, who still feels investigators should have first got a search warrant. "I think you should have an expectation of privacy within your car."

Still, Scott Kidd, senior vice president of Injury Sciences, a Texas firm that provides black-box information to insurers, argues privacy concerns are overblown.

"The data is the data. It's unbiased and objective. The car doesn't care. It's not going to change its data to help one side or the other," Kidd said.

"Our first concern," said Eric Skrum, a spokesman for the National Motorists Association, "is the general public doesn't even know these devices are in their car."

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