Spurred by the Sept. 11 terrorist attacks, airlines and car-rental companies are eyeing biometric, radio-frequency, and global positioning system technologies to identify and track dangerous people and property.

The challenge, though, is to balance their use of technology with citizens' right to privacy. "It's not what technology you use, it's how you use it," says Fred Cate, professor of law at Indiana University and senior policy adviser to the Center for Information Policy Leadership at Hunton & Williams, a Richmond, Va., law firm. Most people are willing to give up some privacy if it means better security for everyone, he says. The problem is if companies use these technologies under the guise of security when the real motivation is the bottom line.

For example, Acme Rent-a-Car in New Haven, Conn., installed a GPS tracking device in its cars, supposedly to track vehicles that were stolen. But then it charged one of its renters $400 in fines for exceeding the speed limit. "The real motivation was to identify ways to make more money," Cate says. In July, Connecticut's Department of Consumer Protection sided with the renter, and Acme didn't collect the fee. Acme still uses GPS, as do several competitors, including Hertz, Budget, and Avis, but only to track stolen cars.

Other applications of technology are more acceptable. Late last month, airports in Indianapolis, Seattle; Portland, Ore.; Amarillo, Texas; and Spokane, Wash., shelled out $300,000 for fingerprint-identification technology from Visionics Corp. to conduct background checks for airport and airline employees starting in the second quarter. Although the plan only targets employees, travelers can also be willing participants. A survey conducted by Harris Interactive in October revealed that 82% of its 2,024 U.S. respondents are willing to have their fingerprints scanned to increase airport security. Nearly two-thirds described fingerprint-identification technology as being extremely or very valuable for airport security.

The respondents weren't as open to facial-recognition technology (see Coming To An Airport Near You?). Only 28% said it'd be an extremely or very valuable enhancement to airport security.

Boston's Logan Airport and Rhode Island's TF Green Airport are testing facial-recognition technology; Fresno Yosemite Airport in California has already deployed it. The American Civil Liberties Union, though, says the technology will harass innocent citizens but let terrorists board planes. The technology can be undermined by people who smile, cover their head with a hat, or wear sunglasses, the group says. The ACLU fears the government will use the technology to monitor innocent citizens-a concern shared by House Majority Leader Dick Armey, R-Texas.

But facial-recognition vendors say the technology doesn't retain images of people who aren't identified on the databases. "Of course we wouldn't scan people with hats on or sunglasses," says Tom Colatosi, president and CEO of Viisage Inc., a biometrics company that's working with Logan and TF Green.

The ACLU sent letters to each airline that was planning to deploy facial- recognition technology, pointing to a government report issued in 2000 that showed a 43% error rate of false negatives. Facial-recognition companies say the technology has greatly improved since the report, which relied on 1999 products.

Airports also are using low-dose X-ray machines, such as Body Search, to scan people. U.S. Customs is using the technology to search for drugs and other contraband. The ACLU is concerned that the searches are being conducted "without good cause and based on profiles that are racially discriminatory." In addition, the ACLU says the machines are capable of projecting an image of a passenger's naked body.

Less controversial is the use of radio-frequency identification tags. In June, San Francisco Airport deployed RFID technology for all checked baggage. The airport check-in system instructs employees to attach a tag to specific pieces of luggage at random or based on red flags raised in the system, such as when passengers pay for their tickets with cash. Once the luggage is placed on the conveyor belt behind the ticket counter, radio-frequency receivers scan the bags as they travel through the maze of conveyers to luggage transport personnel. When a receiver finds RFID-tagged bags, it triggers levers on the conveyor belt to automatically route the bags to a security area where they're screened via cameras and sensors for explosives, chemicals, and hazardous materials.

But RFID-tags have problems, too. Last month, San Francisco Airport was evacuated after the system detected a suspicious bag--but it turned out the bag contained two toy bows and arrows. San Francisco has been testing the technology since July.