Breathalyzers can be made to report a false negative by putting something in your mouth before the test

Breathalyzer Myths

A common myth is that breath testers can be "fooled" (that is, made to generate estimates making one's blood alcohol content appear lower) by using certain substances. An episode of the Discovery Channel's MythBusters tested substances usually recommended in this practice—including breath mints, mouthwash, and onion—and found them to be ineffective. Adding an odor to mask the smell of alcohol might fool a person, but does not change the actual alcohol concentration in the body or on the breath. Interestingly, substances that might actually reduce the BAC reading were not tested on the show. These include a bag of activated charcoal concealed in the mouth (to absorb alcohol vapor), an oxidizing gas (such as N₂O, Cl₂, O₃, etc.) which would fool a fuel cell type detector, or an organic interferent to fool an infra-red absorption detector. The infra-red absorption detector is especially vulnerable to countermeasures, since it only makes measurements at particular discrete wavelengths rather than producing a continuous absorption spectrum as a laboratory instrument would do.

On the other hand, products such as mouthwash or breath spray can "fool" breath machines by significantly raising test results. Listerine, for example, contains 27% alcohol; because the breath machine will assume the alcohol is coming from alcohol in the blood diffusing into the lung rather than directly from the mouth, it will apply a "partition ratio" of 2100:1 in computing blood alcohol concentration—resulting in a false high test reading. To counter this, officers are not supposed to administer a PBT for 15 minutes after the subject eats, vomits, or puts anything in their mouth. In addition, most instruments require that the individual be tested twice at least two minutes apart. Mouthwash or other mouth alcohol will have dissipated after two minutes and cause the second reading to disagree with the first, requiring a retest. (Also see the discussion of the "slope parameter" of the Intoxilyzer 5000 in the "Mouth Alcohol" section above.)

This was clearly illustrated in a study conducted with Listerine mouthwash on a breath machine and reported in an article entitled "Field Sobriety Testing: Intoxilyzers and Listerine Antiseptic," published in the July 1985 issue of The Police Chief (p. 70). Seven individuals were tested at a police station, with readings of .00%. Each then rinsed his mouth with 20 milliliters of Listerine mouthwash for 30 seconds in accordance with directions on the label. All seven were then tested on the machine at intervals of one, three, five and ten minutes. The results indicated an average reading of .43 blood-alcohol concentration, indicating a level that, if accurate, approaches lethal proportions. After three minutes, the average level was still .20, despite the absence of any alcohol in the system. Even after five minutes, the average level was .11.

In another study, reported in 8(22) Drinking/Driving Law Letter 1, a scientist tested the effects of Binaca breath spray on an Intoxilyzer 5000. He performed 23 tests with subjects who sprayed their throats, and obtained readings as high as .81 — far beyond lethal levels. The scientist also noted that the effects of the spray did not fall below detectable levels until after 18 minutes.

Sources:

1. Ayers, Chuck.   "Police React Coolly to 'Breathalyzer' Mints."  The [Allentown] Morning Call.   6 July 1997   (p. B1).
2. Carr-Elsing, Debra.   "Breath Tests for Alcohol Hard to Beat."  Capital Times.   29 December 1992   (p. D1).
3. MacDonald, Peter.   "Ever Been Tempted to Eat Your Shorts?"  The Toronto Star.   10 June 1990   (p. D6).
4. Sarra, Gregg.   "Police Beat."  Newsday.   20 August 2000   (p. G26).
5. Canadian Press.   "Can't Foil Breathalyser With Feces."  The Winnipeg Sun.   30 March 2005.
6. http://urbanlegends.about.com/library/bl_breathalyzer_penny.htm
7. Man Tries to Beat Breathalyzer with Pennies
   Local6.com News, 9 July 2003
8. How a Breathalyzer Works
   By Craig C. Freudenrich, Ph.D., HowStuffWorks.com

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By: lippard on 2008/08/09 AM 10:53:37. The claim is stated to be "false," yet the article shows that it can be "fooled" to produce false positives. Doesn't that show that the claim is true? The claim as written doesn't say "You can fool a breathalyzer into producing a false negative result by putting something in your mouth."