Arrested for drunk driving? A San Diego firm of DUI defense attorneys reports that breathalyzers used by law enforcement do not actually measure alcohol -- and thus may produce falsely high "blood alcohol" readings.

According to the the Law Offices of Lawrence Taylor, Inc., in San Diego, California, most breathalyzers used in DUI cases by law enforcement today use "infrared spectroscopy". This technology involves detection of the "methyl group" in the molecular structure of alcohol. The problem is that there are thousands of chemical compounds containing the methyl group -- some of them found on the human breath. In one study involving 28 subjects, for example, researchers found that the "combined expired air comprises at least 102 various organic compounds of endogenous and exogenous origin" ("Characterization of Human Expired Air", 15 Journal of Chromatographic Sciences 240).

If a person has any of these other compounds on his breath, called "interferents" by the engineers, he will get a falsely high blood-alcohol test result. And if there are two or more such compounds on his breath, the machine will add them up and falsely report the total as the blood- alcohol level.

So what compounds can be found on your breath? According to the San Diego DUI attorneys, diabetics with low blood sugar can have high levels of acetone -- which is "seen" as alcohol by Breathalyzers. And scientific studies have found that people on diets can have reduced blood-sugar levels, causing acetone hundreds of times higher than found in normal individuals (Frank and Flores, "The Likelihood of Acetone Interference in Breath Alcohol Measurements", 3 Alcohol, Drugs and Driving 1). And there are many other so-called "interferents" affecting breathalyzer results

If you are a smoker, your breathalyzer result is likely to be higher than expected. The compound acetaldehyde -- containing the methyl group and so reported by the Breathalyzer as "alcohol" -- is produced in the human body as a by-product in metabolizing consumed alcohol, and eventually passes into the lungs and breath. Researchers have discovered that levels of acetaldehyde in the lungs can be 30 times higher in smokers than in non-smokers. Result: higher BAC readings on the machine.

The San Diego DUI lawyers report that common household products, such as paint, glue, gasoline, and thinners also contain the methyl group. No, you don't have to drink the stuff: simply absorbing it through your skin or inhaling the fumes can result in significant levels of the chemical in your body for hours or even days, depending upon the "half- life" of the compound. So if you've painted a room or breathed in fumes at a gas station in the last day or two, don't take a breathalyzer test.

If you are stopped by the police and suspected of drunk driving, say the San Diego DUI lawyers, you might consider a blood test rather than submitting to a breathalyzer.