Charged with DWI based on a breath test?Houston defense built around the machine, the operator, and the procedural requirements.
The Intoxilyzer 9000 is the breath testing instrument used across Texas DWI cases. The reliability of the result depends on the instrument, the operator, and the procedure — and Texas law requires specific documentation for each. Procedural and scientific challenges to breath-test DWI results are among the most powerful defenses available in Texas.
The Intoxilyzer 9000 is not a black box.
Texas evidentiary breath testing for DWI is governed by 37 Tex. Admin. Code Chapter 19 and the Department of Public Safety’s Scientific Director Rules. The instrument used statewide is the Intoxilyzer 9000, manufactured by CMI, Inc. Like any instrument, it requires calibration, maintenance, and qualified operation to produce reliable results. When those requirements are not met, the result is not reliable.
Texas DPS rules require specific procedures before, during, and after a breath test:
- A 15-minute observation period during which the operator must continuously observe the subject and confirm no foreign substances enter the mouth, no belching, no regurgitation, and no smoking
- Instrument self-checks including an air blank, internal reference check, and ambient air sample before each subject test
- Two subject samples with results that must agree within a specified tolerance
- Periodic instrument certification by DPS Office of the Scientific Director under 37 TAC § 19.4
- Certified operator with a current operator certificate maintained under 37 TAC § 19.3
If any of these requirements is not met or documented, the breath test result may be subject to suppression or exclusion under Tex. R. Evid. 702 or 901.
The most common procedural problems.
Most Intoxilyzer 9000 problems are not problems with the machine itself — they are problems with the procedure surrounding the test. The defense’s job is to find them.
The 15-minute observation period:
This is the single most challenged element. The operator must continuously observe the subject for 15 minutes immediately before the test. “Continuously” means uninterrupted visual contact. If the operator turned away to handle paperwork, escort another arrestee, or operate the instrument controls during the observation period, the requirement may not be met. Body-cam and dash-cam footage often shows exactly what the operator did during this window.
Mouth alcohol contamination:
The observation period exists primarily to prevent mouth alcohol — alcohol residue in the mouth from belching, regurgitation, recent drinking, or dental work — from inflating the breath result. Mouth alcohol can produce a breath result that is multiples higher than the actual deep-lung BAC.
Instrument certification and maintenance:
The Intoxilyzer 9000 must be certified by DPS at regular intervals. Maintenance records, repair logs, and certification documents are subpoenable. If the instrument was out of certification, recently repaired, or producing inconsistent results in the period surrounding the test, the result’s reliability is challengeable.
How a breath-test DWI is defended.
Every breath-test DWI defense begins with the procedural and scientific record. The State must establish a foundation for the breath result before it can be admitted as evidence. The defense’s job is to find the gaps.
Was the observation period continuous?
Body-cam, dash-cam, and jail video are reviewed for the full 15 minutes immediately before the test. Any break in observation can disqualify the result.
Is the operator certified and current?
Operator certificate, training records, and proficiency tests must be in order under 37 TAC § 19.3. An uncertified operator means no admissible result.
Was the instrument properly certified?
DPS instrument certification, calibration, and maintenance records are subpoenable. Out-of-spec or expired certifications affect admissibility.
Was there mouth alcohol?
Belching, regurgitation, recent drinks, dental work, and certain medications can introduce mouth alcohol. If the observation period did not exclude these, the result is suspect.
Do the two samples agree?
Texas requires two subject samples with results agreeing within tolerance. Significant disagreement between the samples is itself a reliability problem.
Medical conditions and breath testing
Acid reflux/GERD, diabetes, and certain diets can affect breath testing accuracy. Where the underlying conditions exist, the result may be challenged on reliability grounds.
The 15-day ALR clock runs the same in breath-test cases.
In breath-test cases, the result is known immediately, so the officer serves a Notice of Suspension (DIC-25) at the scene and a 15-day deadline to request an Administrative License Revocation hearing begins under Tex. Transp. Code Ch. 524. Refusing the breath test triggers a longer suspension (180 days for a first refusal, 2 years for a second). Failing the test also triggers suspension. The ALR is separate from the criminal challenge and runs on its own clock.
SFST certified. Police academy trained. Now defending DWI.
Attorney Kenneth V. Mitchell is SFST certified through the Houston Police Academy and spent 13 years as a Texas police officer — including service in the Hit and Run and Vehicular Crimes Division of the Houston Police Department. He has personally observed evidentiary breath tests in the field and understands the procedures from the operator’s side.
For a breath-test DWI, that experience matters. Cross-examining the breath test operator about the 15-minute observation, the instrument self-checks, and the procedural compliance requires knowing what should have happened. Kenneth knows what should have happened because he has been on the operator’s side of the same procedure.
Blood-test DWI cases turn on gas chromatography, chain of custody, and warrant issues. See DWI blood test defense.
The number is not the whole story.
A breath test result is only admissible if the procedural and scientific foundation supports it. Every observation period, every instrument certification, every operator credential, every machine self-check is part of that foundation. The defense’s job is to find the missing piece.
Free, confidential case review. Flat-fee breath-test DWI defense across Harris, Montgomery, and Galveston Counties. Kenneth reviews every breath-test DWI inquiry personally.