FREDERICKSBURG, Va. - A motorist eases to a stop at a sobriety checkpoint and rolls down his window. A police officer thrusts the illuminated end of a flashlight six inches from the driver's face and starts asking questions.
Unbeknownst to the motorist, a tiny, battery-powered device on the end of the flashlight is sucking in his breath and analyzing it for traces of alcohol.
Civil liberties groups say it's an invasion of privacy, a violation of the spirit, if not the letter, of the Fourth Amendment's protection against unreasonable search and seizure.
Police and the manufacturer of the ''P.A.S. III Sniffer'' disagree. They say the gadget - used by hundreds of police agencies nationwide - is merely an extension of the officer's nose, and nobody's ever questioned the propriety of police sniffing out drunken drivers.
''We like what we're doing,'' said Jarel R. Kelsey, president of PAS Systems International, based in a nondescript brick building in Fredericksburg. ''There's a well-established need for this technology. You just have to look at the statistics on alcohol-related traffic deaths.''
According to the National Highway Traffic Safety Administration, 15,935 people died in alcohol-related crashes in 1998, making up 38.4 percent of all traffic deaths in the United States.
But the executive director of the American Civil Liberties Union in Virginia, Kent Willis, said that while getting drunken drivers off the highways is a noble cause, it should not come at the expense of privacy.
''Where will we finally draw the line? Why not just fight crime by creating adult curfews and randomly searching houses? Both would assist in crime fighting but would be a dramatic blow to privacy rights,'' Willis said.
Covert use of the Sniffer amounts to entrapment, said John Whitehead, president of the Rutherford Institute, a civil liberties group based in Charlottesville.
''They're reaching into your vehicle with an electronic device,'' Whitehead said. ''That's the sort of thing you expect in Eastern Bloc countries or Communist China, not the United States.''
The Sniffer has been on the market since 1993. For daytime use when the flashlight isn't appropriate, the company also sells a clipboard containing an alcohol sensor.
The constitutionality of the Sniffer has never been tested in court. Kelsey said his company has done considerable research on the issue and he is confident the device would withstand a legal challenge.
He said it falls under the ''plain sight doctrine,'' which holds that observations an officer makes with his senses do not violate the Fourth Amendment. The doctrine applies whether the officer collects the air sample with his unaided nose or with the Sniffer, Kelsey said.
The Fairfax County police department has 21 Sniffers for its force of more than 1,200 officers, said Jerry Stemler, coordinator of anti-drunken driving programs for the department.
''The big advantage is they're able to detect alcohol in the air where an officer may not for one or more reasons,'' Stemler said.
For example, an officer's sense of smell might be dulled by a cold or allergies, or a brisk wind might blow alcohol fumes away.
Nobody is arrested based solely on a positive reading by the Sniffer. If the device indicates alcohol in the air sample, the driver is held for further tests.
''It's quick, it's noninvasive, and it protects the safety of the officer'' because he doesn't have to get right in the driver's face, said Simon Stapleton, executive director of the Virginia chapter of Mothers Against Drunk Driving.
On the Net:
PAS Systems International: http://www.sniffalcohol.com
Mothers Against Drunk Driving: http://www.madd.org
Rutherford Institute: http://www.rutherford.org
American Civil Liberties Union: http://www.aclu.org