Recent news about an area woman's arrest for driving after drinking one (1!) glass of wine could toss cold water on local holiday celebrations. Two inexpensive personal breathalyzer gadgets, available online and in some stores, claim to help drivers determine whether they belong behind the wheel. Is this a good idea -- or is using one of these evidence of impaired judgment?

Blow Hard The units are the Alcohawk Checkpoint ($24.99 for 12 single-use tubes) and the Legal Limit Breathscan ($3.99 for a key chain holder and one tester, refills $2.99 each; www.saveabuddy.com). The devices measure blood alcohol content (BAC) by analyzing breath from deep in the lungs. To get a reading, users exhale into the device for about five seconds. Chemically coated yellow crystals turn greenish-blue when the breath that comes in contact with them has a specified BAC. Both testers can be purchased in versions that detect levels from 0.02 (barely a glass of wine) to 0.08 (most states' limits for defining impairment).

Test Drive Have these things kept any drivers from making a dumb decision? "We're not aware of any systematic research" on their effectiveness, said Ruth Shults, a senior epidemiologist at the National Center for Injury Prevention and Control, part of the Centers for Disease Control and Prevention (CDC). Disposable testers are expected to be distributed for use in bars as part of a CDC-funded study on designated drivers. Shults describes the devices' role as "a very small part of a much larger intervention campaign."

If You Have to Ask . . . Though some reports vouch for the accuracy of certain handheld testers, many experts say that self-testing is not a good idea. (Legal Limit is marketed as a device for testing a possibly drunk friend.) An accurate reading depends on breathing properly, and "if you're impaired, you're more likely to mess it up," said Robert Shesser, chairman of emergency medicine at George Washington University Hospital. His advice: If you've been drinking and "think you should take a breathalyzer test, you shouldn't be driving."

-- Matt McMillen

Disposable breathalyzers like the Legal Limit Breathscan can detect blood alcohol. But if you have to test, don't drive.