In the past, someone arrested for driving under the influence of alcohol (DUI) used to be given a choice of three tests to verify the amount of alcohol in their system: a blood, breath, or urine test. Since then, urine tests have been found to be unreliable for concentration amounts. Blood tests are invasive and involve a needle. Because of this, a breath test has been the preferred choice by law enforcement and the accused.
To take a breath test, a person blows into a machine, called an intoxilyzer, and the machine figures out how much alcohol is in their blood. If the result is a .08% blood alcohol content (BAC) or higher, then the person is deemed intoxicated and not safe to operate a vehicle. A result lower than a .08% infers that the person may be safe to drive, but that can be challenged by the person's driving pattern and other factors.
An intoxilyzer is a machine, and is subject to problems, like any other machine. Sometimes the results are not accurate, the machine may need calibration, and there is an expected variation in results. Also, the operator must be trained and certified, and needs to keep the certification current. There are also rules governing an observation period prior to administering the test to make sure that there is no alcohol in the test subjects mouth from burping or regurgitation that could effect the validity of the test.
If you have been arrested for DUI, and had to take a breath test, this fact will be explored in both the Drivers License Hearing and the prosecution of the criminal DUI charges. I have successfully represented clients in challenging the validity of the intoxilyzer test results based on the problems with the technology, the failure of a police officer to follow the mandatory protocols, and the failure of the officer to keep his certification current. As a result, I have been able to help my client's keep their drivers licenses, and avoid criminal convictions.