A lawyer challenges breathalyzer evidence by digging into the machine, the procedure, and the biology behind the reading. A breath number is only as reliable as the process that produced it, and that process is run by people using equipment that can fail.
The first thing to request is the paperwork. Every breath device has to be calibrated and maintained on a set schedule, with accuracy checks logged. If those records show missed calibrations or failed checks, the reading becomes suspect. California's Title 17 regulations spell out exactly how a breath test must be run, and any deviation is a point of attack.
Procedure matters just as much. The officer is supposed to observe you for about 15 minutes before the test to make sure you don't burp, belch, or regurgitate, which can push mouth alcohol into the sample and spike the result. Officers routinely cut that period short.
Then there's biology. A breath machine assumes one conversion ratio for everyone, but real bodies vary. Acid reflux, GERD, diabetes, ketosis from a low-carb diet, and even residual mouth alcohol can all inflate a reading. When the science gets deep, a forensic toxicologist can testify to what really happened.
You can read more about these fights on the BAC defense page and the refusing a breath test page.
This is general information, not legal advice. For a free look at your breath records, call (858) 622-7280 or visit /contact.