By Suzuki Law Offices · July 30, 2026 12:03 PM (GMT+5:30)
Have you been stopped by the police in Phoenix and told that your breathalyzer result shows you over the legal limit? If so, you might feel like the evidence against you is ironclad. The truth is, breathalyzer tests are far from perfect. They rely on sensitive equipment and strict protocols that can fail in many ways. Understanding the potential flaws in your test is the first step toward building a strong defense. A skilled DUI attorney Phoenix can evaluate your case and identify whether the result is worth challenging.
Breathalyzer devices measure the amount of alcohol in your breath, then convert that number into an estimated blood alcohol concentration (BAC). This conversion assumes a fixed ratio of breath alcohol to blood alcohol — 2100:1 — but that ratio varies from person to person by as much as 15% to 20%. That means two people blowing the same number could have very different actual BACs. In addition, the device must be properly maintained, regularly calibrated, and operated by a trained officer. When any of those conditions break down, the result becomes unreliable. When you are looking for a challenges to breathalyzer tests, make sure the attorney focuses on these technicalities and can often persuade a judge to exclude the breath test from evidence. This is often where phoenix dui lawyer proves its value in practice.
But what specific flaws should you look for? Let's break down the most effective ways to challenge a breath test, from machine problems to human mistakes. You will see that even an apparently high reading may have an explanation that undermines the prosecution's case. Many teams turn to dui attorney phoenix to handle exactly this kind of workload.
Every breathalyzer used by law enforcement in Arizona must undergo periodic calibration to ensure accuracy. Calibration means adjusting the device so that it correctly analyzes a known alcohol concentration — typically a "simulator solution" with a certified alcohol content of 0.10% BAC. If the device reads that test sample within a narrow tolerance, it is considered accurate. However, if calibration drifts even slightly, the results for actual drivers can be falsely high or falsely low. In Arizona, agencies can be required to produce calibration logs. If those logs show inconsistencies, missed calibration dates, or out-of-tolerance readings, your DUI lawyer Phoenix can move to suppress the evidence. For example, if a machine was last calibrated three months before your arrest but the manufacturer recommends monthly calibration, that is a clear failure to follow standards. A court may rule the test inadmissible. When this becomes a priority, dui lawyer phoenix can make a real difference to your results.
Beyond regular calibration, the device must also pass a "control test" before each use. The officer runs a test with a known alcohol sample. If that control test is not performed or the results are not recorded, it becomes another avenue for challenge. In some cases, a lawyer might subpoena the maintenance records and demonstrate that the machine has a history of false positives. This kind of evidence can be very powerful, especially if the device is an older model known for stability issues.
Even a perfectly calibrated machine will produce inaccurate results if the officer administering the test makes mistakes. Arizona law requires officers to observe the subject for at least 15 to 20 minutes before the test to ensure no alcohol, food, or smoke enters the mouth during that period. This is called the "deprivation period" or "observation period." If the officer did not watch you continuously — for example, if they turned away to write notes or talk to another officer — then the test result could be compromised. A Phoenix DUI lawyer will ask the officer directly on the stand: "Did you keep your eyes on me the entire 20 minutes?" If the answer is no, that's a flaw.
