In most Arkansas DWI cases, the breathalyzer number is the State’s single most important piece of evidence. Prosecutors treat it as objective and scientific. Jurors tend to believe it. But breath testing machines are not infallible — they’re machines, operated by humans, under regulations that are not always followed.
Here’s how breath testing actually works in Arkansas, where the accuracy problems come from, and how an experienced defense attorney challenges a breath test result.
The Core Point
A breath test result is not self-proving. For the number to come into evidence, the State must show the machine was properly certified and maintained, the operator was properly certified, and the test was administered according to Arkansas Department of Health regulations. Each of those requirements is a place where cases are won.
How Breath Testing Works in Arkansas
There are two very different breath tests in a typical Arkansas DWI case, and the distinction matters:
| Test | When | Legal Status |
|---|---|---|
| Portable Breath Test (PBT) | Roadside, before arrest | Voluntary. Generally used only for probable cause — the number is typically not admissible at trial to prove BAC. |
| Evidentiary Breath Test | At the station, after arrest | Covered by implied consent. This is the number the State uses at trial. |
The evidentiary test in Arkansas is administered on an approved instrument — commonly the Intoxilyzer — under the oversight of the Arkansas Department of Health (ADH), which regulates breath testing statewide. ADH rules govern which instruments are approved, how they’re calibrated and maintained, who may operate them, and how the test must be administered.
Why Breath Tests Get It Wrong
Breath machines don’t measure blood alcohol directly. They measure alcohol in breath and use a conversion ratio to estimate blood alcohol. Every step of that process introduces potential error:
Calibration Drift
Machines drift out of calibration over time. If calibration checks were missed, late, or failed, the reading is suspect.
Mouth Alcohol
Burping, belching, acid reflux (GERD), vomiting, dentures, or recent drinking can put raw alcohol in the mouth — producing falsely high readings that don’t reflect blood alcohol.
Rising BAC
Alcohol takes time to absorb. Your BAC at the station may be higher than it was when you were driving — and the State must prove your BAC at the wheel.
Partition Ratio Variability
Machines assume a standard breath-to-blood conversion ratio. Actual ratios vary between individuals and even within the same person over time.
Physiological Factors
Body temperature, breathing pattern, lung capacity, and certain medical conditions (diabetes, ketosis, GERD) can all skew results.
Radio Frequency & Environmental Interference
Electronic interference and environmental contaminants in the testing room can affect some instruments.
None of this means every breath test is wrong. It means a breath test number is an estimate produced under conditions that must be proven correct — not an unchallengeable fact.
The Arkansas Requirements the State Must Prove
For a breath test result to hold up in an Arkansas courtroom, the State generally needs to establish:
- Approved instrument. The machine must be an ADH-approved device.
- Current certification and maintenance. The specific machine must have current certification, with calibration checks and maintenance documented in its records.
- Certified operator. The officer administering the test must hold a current ADH operator certification.
- Proper observation period. The subject must be continuously observed before the test to ensure nothing happens (burping, vomiting, putting anything in the mouth) that could contaminate the sample. If the officer was doing paperwork, in and out of the room, or transporting the subject during the “observation,” the observation period can be attacked.
- Proper administration. The test sequence itself must follow the required protocol.
Every one of these is documented somewhere — machine logs, calibration records, certification cards, station video. A defense attorney’s first move in a breath test case is requesting all of it.
The Two-Hour Issue
Timing matters in Arkansas breath testing. When a test is administered promptly, the State benefits from a presumption connecting the result to the time of driving. When testing is significantly delayed — Arkansas case law has addressed tests administered more than two hours after the relevant driving — the connection between the number and your BAC at the wheel weakens considerably.
A delayed test opens the door to the rising BAC defense: if you drank shortly before driving, your BAC may have still been climbing when you were stopped — meaning the station reading could be higher than your BAC while actually driving. The State must prove your BAC at the time of driving, not at the time of testing. In borderline cases (0.08–0.10), this argument alone can create reasonable doubt.
Your Right to an Independent Test
Arkansas law gives a person who submits to the State’s chemical test the right to obtain an additional independent test administered by a qualified person of their own choosing. Law enforcement is required to advise you of this right and provide reasonable assistance (such as access to a phone) in obtaining it.
This matters for two reasons. First, an independent blood test can directly contradict a flawed breath result. Second, if police failed to advise you of the right or obstructed your attempt to exercise it, that failure itself can become a defense issue. Few defendants know this right exists — which is exactly why it’s worth asking about in every breath test case.
How a Defense Attorney Challenges a Breath Test
A breath test challenge is built from records, not speculation. The typical sequence:
1. Request the Machine’s Records
Calibration logs, maintenance history, certification records, and any repair or error history for the specific instrument used — not just a blanket “the machine was certified” statement.
2. Verify the Operator’s Certification
Was the officer’s ADH operator certification current on the test date? Expired or lapsed certification is a direct admissibility problem.
3. Reconstruct the Observation Period
Station video, body-cam, and booking records often show the “continuous observation” wasn’t continuous — the officer was filling out paperwork, the subject burped or belched, or the period was cut short.
4. Build the Timeline
Time of driving, time of stop, time of test. Delay supports rising BAC arguments; drinking history and food intake fill out the absorption picture.
5. Screen for Medical Factors
GERD, diabetes, dental work, recent illness — conditions that create mouth alcohol or skew readings get developed through medical records and, when warranted, expert testimony.
6. File the Right Motion
Depending on what the records show, the remedy may be a motion to suppress the result entirely, a motion in limine limiting how it’s presented, or cross-examination that reduces the number’s weight with the jury.
And remember — the breath test is only one layer of the case. The legality of the stop, the field sobriety tests, and the arrest itself all come first. If the stop or arrest was unlawful, the breath test result can fall with them regardless of how the machine performed.
What About Blood Tests?
Blood tests are generally more accurate than breath tests, but they have their own challenge points: chain-of-custody gaps, contamination or fermentation of the sample, lab procedures, and warrant issues. Under Birchfield v. North Dakota, police generally need a warrant (or valid consent) for a blood draw. A warrantless, nonconsensual blood draw is a serious constitutional problem for the State.
The Bottom Line
The breathalyzer number feels final to most people who get arrested. It isn’t. It’s an estimate, produced by a machine that requires proof of calibration, operated by a person who requires proof of certification, under procedures that require proof of compliance — connected to your driving by a timeline the State has to establish.
In borderline cases especially, a properly developed breath test challenge can be the difference between a conviction and a dismissal. The records that make these challenges possible need to be requested early — before they become harder to obtain. For the full picture of what happens after a DWI arrest, see our step-by-step first-offense DWI guide.
Failed a Breath Test in Arkansas?
A breath test number is challengeable — but only if the machine records, certification documents, and station video are requested before they’re gone. And remember: you have just 7 days from arrest to request your license hearing.
This post is provided for general informational purposes only and does not constitute legal advice. Reading this content does not create an attorney-client relationship with Wesley Rhodes, Attorney at Law. Laws and procedures change; the information above reflects Arkansas and federal law as of the date of publication. If you need legal advice about your specific situation, consult a qualified criminal defense attorney promptly.