Fisher Law Office

Understanding roadside breath testing machines

You probably already know that your blood alcohol concentration here in California cannot legally exceed .08. You also know that police officers may ask you to submit to a breath test on the side of the road during a DUI traffic stop.

What you may not know is that there is a significant margin of error of up to 15 percent for roadside breath testing machines. That may not seem like a large number, but if you are one of the 23 percent of drivers arrested for DUI based on a false positive, it could make all the difference.

Not all breath testing machines are alike

The type of machine used by a particular police department could increase the risk of false results. Breath testing machines fall into one of the three following categories:

  • Infrared machines use light wavelengths to determine the amount of ethanol in your system. These machines tend to cost less, so many departments use them.
  • Fuel cell breath testing machines use electrical current to measure the amount of ethanol in your system. The industry considers this type of machine as the most accurate.
  • Color-changing breath testing machines use chemicals that determine the amount of alcohol in your system. The more color change, the higher your BAC supposedly is.

You could even purchase your own breath testing machine to see whether you should drive on a particular night, and it may be just as accurate as the one used by police officers on the side of the road. Knowing this, you can see why the results may be inaccurate.

What can go wrong with roadside breath tests?

Any number of issues with you and the environment could cause false positives. Consider the following:

  • Your body temperature, blood composition and other factors such as the following can affect the outcome of a breath test:
    • Diabetes
    • Vomit in your mouth
    • Blood in your mouth
    • Breath fresheners
    • Mouthwash
    • Acid reflux
    • Alcohol residue in your mouth
  • Your environment can also affect the outcome of any testing. For instance, the following environmental factors are known to interfere with testing:
    • Smart phones
    • Police radios
    • Paint remover
    • Cleaning fluids
    • Vinegar

The bottom line is that roadside breath testing machines are not infallible. Just because an officer tells you that your reading came back above the legal limit, it does not mean that you should not challenge the results of the test. In fact, having the above information may be the first step on your list of things to do when it comes to your defense.

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Fisher Law Office

1322 Morro Street
San Luis Obispo, CA 93401-4028

Phone: 805-706-0205
Fax: 805-542-0464
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