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Law Offices of Matthew C. Bishop, Inc.
Serving Napa, Marin And Solano Counties

Are Breathalyzers always accurate?

If authorities pull you over on suspicion of drunk driving in California, you can expect that the law enforcement official who does so will ask that you submit to a breath test using a device called a Breathalyzer. When properly used and maintained, Breathalyzers are often accurate, but there are a number of outside circumstances that can impact accuracy. Because the repercussions associated with drinking and driving are so severe, you want to be sure that there is no question about the validity of the results of your breath test.

According to, there can be a 15-percent variation between the blood-alcohol content reading a Breathalyzer provides and what is actually accurate. In some cases, this fluctuation is attributed to improperly calibrated Breathalyzers, as regular calibration is required to ensure that the devices are not impacted by ambient or subject temperatures, or other outside factors.

Electronic interference also has the capacity to lead to a falsely elevated Breathalyzer reading, and it can come from a number of different sources. In some cases, those charged with drinking and driving have blamed police radios for false Breathalyzer readings, but cellphone signals, too, can affect Breathalyzer accuracy. If you have blood or vomit in your mouth when you take your breath test, know that this, too, can lead to a false reading. Typically, law enforcement officials know this, and they also know to wait for 20 minutes or so after noticing blood or vomit before attempting to re-administer your breath test.

This information about Breathalyzer accuracy seeks to inform you, but it is not a replacement for legal advice.

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Law Offices of
Matthew C. Bishop, Inc.

1810 Jefferson Street
Napa, CA 94559
Phone: 707-266-6952
Fax: 707-255-3612
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