You blew a number. The officer acted like the case was over. It isn’t.
A breath test result feels like scientific proof: a machine spat out a number, and the number is over 0.08. But as Jay Cohen learned earning the ACS-CHAL Forensic Lawyer-Scientist designation, the machine doesn’t measure your blood alcohol at all. It estimates it, from your breath, using assumptions about the “average” human body that may be flat wrong for yours.
How the Machine Guesses
Texas uses the Intoxilyzer 9000. It shines infrared light through your breath sample and infers a blood alcohol level using a fixed conversion ratio applied to everyone, regardless of your body temperature, breathing pattern, lung capacity, or medical conditions. When your body doesn’t match the machine’s built-in assumptions, the number moves, and for some people it moves up.
Ways a Breath Score Goes Wrong
- Mouth alcohol. A burp, reflux (GERD), or even dental work can put raw alcohol in your mouth, and a required 15-minute observation period exists precisely because of it. On video, we often see officers start the test well before the 15 minutes are up.
- Ketosis. Low-carb dieters and diabetics produce compounds that infrared analysis can misread as ethanol.
- Machine maintenance and calibration. Every Intoxilyzer has maintenance records, error logs, and reference-sample history. We subpoena all of it. A machine with a spotty logbook makes a lousy witness.
- Operator error. The operator needs a current certification and has to run the protocol exactly. “Mostly right” doesn’t cut it when your record is on the line.
- Instrument error codes and invalid-sample flags that never made it into the officer’s report.
What We Do With All That
We don’t wave our hands and say “machines make mistakes.” We pull the data (maintenance logs, calibration records, the officer’s certification, the observation-period video) and we build the specific, documented reasons your number can’t be trusted. Then the State has a problem: its whole case was the number.
The legal question is whether you were intoxicated while you were driving, and a breath test taken an hour after the stop measures the wrong moment.
Watch: Breath test results explained
Two short explanations of how breath test evidence actually works in a Texas DWI case, and what your options are at the roadside.
Blowing under .08 is not a free pass
Should you blow into a roadside portable breathalyzer?
Breath Test FAQs
How accurate are breathalyzers, really?
Even under ideal lab conditions, breath testing carries a recognized margin of error, and roadside conditions are never ideal. For a score near the legal limit, that margin alone can be the whole case.
I blew over 0.15. Is it hopeless?
No. Higher scores raise the stakes (Class A misdemeanor territory for a first offense) but they don’t make the machine more trustworthy. Some of our best outcomes started with ugly numbers. Prior results do not guarantee a similar outcome.
Can I still fight the license suspension?
Yes, but only for 15 days. See our Houston ALR hearing lawyer page and don’t sit on it.
Put the Machine on Trial
The breath test is the State’s favorite witness, and it can be cross-examined. If your case involves a blood draw instead, see how we challenge DWI blood tests. Call our Houston DWI lawyer team at (713) 664-4000 for a free, confidential consult.
Reviewed by Jay Blass Cohen, founder of Blass Law PLLC, ACS-CHAL Forensic Lawyer-Scientist, certified Drug Recognition Expert, and SFST instructor, serving Houston since 2009. This article is general information, not legal advice for your situation. Prior results do not guarantee a similar outcome.