The Traffic Stop Wasn’t Legal
Every DUI case starts with a traffic stop, and that stop must be legally justified. An officer needs reasonable suspicion — a specific, articulable reason to believe a traffic violation or criminal activity occurred — before pulling you over. Weaving slightly within your own lane, for example, has been found insufficient for a legal stop in some jurisdictions. A hunch isn’t enough. A quota isn’t enough.
If the stop itself was unlawful, everything that followed is tainted. Field sobriety test results, breathalyzer readings, the officer’s observations — all of it can be suppressed under the exclusionary rule. Without that evidence, prosecutors often have no case left to bring. Challenging the constitutionality of the stop is one of the first things an experienced DUI attorney examines.
The Breathalyzer Results Are Unreliable
Breathalyzer devices are not infallible. They require regular calibration, proper maintenance, and trained operators. When any of those requirements aren’t met, the BAC reading they produce is scientifically questionable — and courts have thrown out breath test results on exactly these grounds.
Your attorney can request the maintenance and calibration logs for the specific device used in your arrest. If the device was overdue for calibration, had a recorded malfunction, or was operated by an officer without current certification, that creates a legitimate basis for challenging the result. A BAC reading close to the legal limit becomes especially vulnerable when the device itself has a documented margin of error.
Field Sobriety Tests Were Administered Incorrectly
Standardized field sobriety tests — the walk-and-turn, the one-leg stand, the horizontal gaze nystagmus test — must be conducted according to protocols established by the National Highway Traffic Safety Administration. Deviation from those protocols directly affects the validity of the results.
Beyond procedural errors, these tests are affected by factors that have nothing to do with alcohol: an uneven road surface, poor lighting, footwear, inner ear conditions, age, weight, and anxiety can all affect performance. An attorney who understands the science behind these tests can challenge both how they were administered and what the results actually demonstrate.
Blood Test Handling Was Improper
Blood evidence is only as reliable as the process used to collect, store, and analyze it. If the sample wasn’t drawn by a qualified phlebotomist, stored at the correct temperature, or analyzed using approved laboratory procedures, the results can be challenged — and in some cases suppressed entirely. Chain of custody errors are more common than people realize and can be decisive in close cases.
The Bottom Line
A DUI charge is not a guaranteed conviction. The evidence that supports these charges is technical, procedural, and frequently imperfect. Finding the imperfections requires an attorney who knows where to look — and that’s exactly why the attorney you choose matters so much from the very beginning.