The primary roadside tool used by law enforcement officers in the enforcement of DUI laws is the Preliminary Breath Test (PBT) or Preliminary Alcohol Screening (PAS) breathalyzer device. These small devices can be easily held in one hand. The officer instructs the driver blow into a mouthpiece on the device. This testis conducted twice enabling the officer to confirm a consistent result. Remember, in California, a driver does not have to submit to a roadside breathalyzer test unless he or she has been arrested. And even after an arrest, the driver still is not required to submit to the roadside test but may request a blood test or a breath test on the more accurate breath testing machine located in all law enforcement stations. The breath test machines at police stations are larger devices and produce more accurate results than the roadside devices. Despite some of the stories you may have heard, it is virtually impossible to fool the roadside breathalyzer or the breath testing machine at the police station.

All blood alcohol content breath testing machines use either fuel cell or infrared cell technology. The cell sensors on the machines oxidize the alcohol in the breath sample, which produces an electrical current that the breathalyzer is able to measure and translate into the percentage of alcohol in the persons system. Unless you are a chemist, this all sounds rather confusing but it may be enough to say that the alcohol in a person’s blood vaporizes and passes through the lungs. I discussed this process in an earlier post. These organic compounds passing through the lungs are measurable as wavelengths of alcohol.

Breathalyzers can produce inaccurate results. This may occur when the machine itself is not properly calibrated or defective. False-positive results may also appear on the machine due to the presence of alcoholic compounds in a person’s system that show up as ethyl alcohol molecules—the molecules that the breathalyzer detects—when, in fact, the alcohol molecules detected are part of the wider spectrum of methyl alcohol. Ethyl alcohol, the compound that is found in alcoholic drinks is only one molecule in a broader array of alcoholic compounds. For example, a person who suffers from certain medical conditions or who is taking a prescription medication may test positive on an alcohol detection breath test even though he or she has not been drinking. However, there are newer devices being put into operation that are able to distinguish between these various methyl alcohol compounds.

Breath test results are almost always the primary evidence used to prosecute a person for driving under the influence. While these tests are generally considered accurate, it may be possible to challenge the results and that is especially true when the result is very close to blood alcohol content thresholds.

In those cases where a driver tests positive on a breath test and he or she believes it is due to medication or some other condition, it is important to request a blood test. This may not always be possible if the driver declined the roadside breathalyzer and submitted to the breath test at the station, rather than requesting a blood test. While it is usually advisable to decline the voluntary (pre-arrest) roadside breathalyzers, if a driver have not been drinking, he or she should take the roadside test. If it comes up positive at least then the driver can then request a blood test at the station.

If you have been arrested for DUI and believe your breath test was inaccurate, you should consult with an attorney experienced in defending these types of cases right away. William Weinberg has been defending those charged with driving under the influence for almost 25 years. He offers a complimentary consultation on any DUI or criminal matter. You may contact Mr. Weinberg at his Irvine office at (949)474-8008 or by emailing him at