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Florida DUI Defense Attorney > Blog > DUI Defense > How Does Breath Testing Work?

How Does Breath Testing Work?


Under Florida law, if an officer requests a breathalyzer test, implied consent rules mean that you cannot refuse the test without the law presuming you are guilty of driving under the influence of alcohol. However, breathalyzer tests are not the most accurate way to measure BAC, and they do have a margin of error. In Florida, the most common device used to measure BAC is the Intoxilyzer 8000. This device measures the amount of ethyl alcohol in your breath using an infrared sensor.

The logic of the test works on the belief that the amount of alcohol in your breath is directly related to the amount of alcohol in your blood stream. Nonetheless, testing the blood directly is the most accurate way to determine BAC. Because breath alcohol must be converted to blood alcohol, there is a margin for error with these tests.

How does the test work? 

The Intoxilyzer 8000 measures infrared absorption of substances with wavelengths in the 3.39 to 3.48 micron range. However, ethyl alcohol is not the only substance that triggers positives in this range. One common molecule that will also trigger a positive in this range is acetone which is present on the breath for those who are on the keto diet. In other words, those who are on a low-carb diet can trigger inflated BAC scores.

While ethyl alcohol remains the most likely reason that the test will trigger a positive, it is not impossible that a test would inflate the score of a suspect who is below the legal limit for alcohol consumption. This is especially true for those who are on a low-carb diet. Further, fumes inhaled can also trigger positives. So, it isn’t a precise science when it comes to measuring BAC.

Blood tests are the most accurate measure 

If your BAC is at or near the legal limit of .08, you can request that a blood test be performed. You can also dispute the results of a breathalyzer test that is very close to the legal limit because there is a range of error associated with these tests. In some cases, the devices aren’t calibrated properly which can also give rise to false positives. In these cases, a defendant who is charged with DUI will have some wiggle room to either get the charges against them dropped or plead the case down.

Blood tests are considered the most accurate way to measure BAC. In the case of a blood test, you are measuring the blood directly as opposed to comparing breath alcohol to blood alcohol. If your BAC is at or near the legal limit, you can request an independent blood test to ensure that you are actually over the legal limit as opposed to a false positive.

Talk to an Orlando DUI Attorney Today 

FL DUI Group represents the interests of those who have been charged with DUI. If a breath test says you are near the legal limit, you may be able to dispute the results of the test. Call our Florida DUI defense lawyers today to schedule an appointment and we can begin discussing your defense options immediately.

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