When someone is arrested for driving while intoxicated (DWI) in Missouri, one of the most critical pieces of evidence law enforcement relies on is the result of a breathalyzer test. These roadside or station-based tests are used to measure your blood alcohol concentration (BAC), and prosecutors often present the results as key proof that you were legally impaired. But are these breathalyzer results always allowed in court? The answer is not necessarily. While breath test evidence can be powerful, it is not immune to challenge. 

In Missouri, specific legal standards and procedures must be met for the results to be admissible. If law enforcement fails to follow these rules precisely, your attorney may be able to get the results thrown out, dramatically weakening the prosecution’s case.

What Missouri Law Says About Breathalyzer Admissibility

The admissibility of breath test results in Missouri DUI cases is governed in part by Missouri Revised Statute § 577.021. This law outlines the basic conditions under which chemical test results, including breath, blood, and urine, can be submitted as evidence in court. Under this statute, for a breathalyzer result to be admissible:

• The test must be administered by a person holding a valid permit issued by the Missouri Department of Health and Senior Services (DHSS).
• The device used must be approved by the DHSS and maintained according to state regulations.
• The test must be conducted in substantial compliance with DHSS standards and procedures.

If these conditions are not met, your lawyer can file a motion to suppress the breathalyzer result, arguing that it does not meet the minimum requirements for reliability and fairness in court.

What Can Make a Breathalyzer Inadmissible?

Breath tests may seem scientific and foolproof, but in reality, several factors can render them unreliable or legally inadmissible. Here are common reasons a breathalyzer result may be challenged:

• Improper calibration: Breathalyzer devices must be regularly calibrated to ensure accuracy. If the maintenance log is missing or incomplete, the results can be disqualified.
• Operator error: The officer administering the test must be properly trained and certified. Any deviation from protocol may be grounds to exclude the results.
• Device approval issues: Missouri only permits the use of specific, approved breathalyzer models. If a non-approved device was used, the results may be thrown out.
• Failure to observe before testing: Missouri requires a 15-minute observation period before administering a breath test. If this period is skipped or undocumented, the result may be considered unreliable.
• Medical or environmental interference: Conditions like acid reflux or the presence of certain chemicals can affect test accuracy and may be cited as a defense.

At The Law Office of Denise Kirby, we thoroughly investigate every aspect of the test, including equipment logs, officer credentials, and procedural documentation, to find any weaknesses that can benefit your defense.

How Breathalyzer Results Are Used Against You

In Missouri, if your breath test shows a BAC of 0.08% or higher, that alone can be used as presumptive evidence of intoxication. This means prosecutors don’t need additional proof of impaired driving behavior; they can rely solely on the breathalyzer reading. However, this doesn’t mean your case is hopeless. 

Challenging the validity of the breath test can eliminate that presumption and force the prosecution to rely on other, often weaker, forms of evidence such as officer observations, field sobriety tests, or dashcam footage. That’s why breathalyzer challenges are a cornerstone of many successful DUI defense strategies.

What Happens if the Breath Test Is Suppressed?

If your attorney succeeds in getting the breathalyzer result suppressed, the prosecution loses one of its most compelling pieces of evidence. In some cases, this can lead to reduced charges or even a complete dismissal, especially if there is no other strong evidence showing that you were impaired. Even when the breath test isn’t thrown out entirely, undermining its credibility can be enough to raise doubt in the mind of a judge or jury. That doubt can be critical in DUI trials, where the burden of proof is on the state.

Should You Still Submit to a Breath Test?

Missouri’s "implied consent" law requires drivers to submit to chemical testing if an officer has reasonable grounds to believe they are driving under the influence. Refusing to take the test results in automatic administrative penalties, including a one-year license revocation and mandatory installation of an ignition interlock device for reinstatement. However, a refusal may also eliminate breathalyzer evidence from your criminal trial. This makes refusal a complicated issue that must be weighed carefully based on your unique situation and criminal history.

If you've been arrested for DWI in Missouri and submitted to a breath test or refused one, don’t assume the case is open and shut. There may be serious flaws in the evidence against you. Our DWI defense attorneys know how to identify and expose those weaknesses. Contact us today to schedule a consultation and start building your defense with a legal team that understands Missouri DUI law inside and out.