DWI Breath Test Issues: Machine Calibration, Operator Errors, and Legal Defenses (2025)

When you're charged with Driving While Intoxicated (DWI), a breath test reading showing a blood alcohol concentration (BAC) of 0.08% or higher can seem like an open-and-shut case — but the reality is far more complex. Breathalyzers are highly sensitive instruments that require strict calibration, careful operation, and adherence to legal protocols to produce accurate and admissible results. From machine malfunctions and software glitches to untrained officers and overlooked medical conditions, numerous factors can cause false or inflated readings. 

In this guide, we’ll break down the most common DWI breath test issues — including machine calibration errors, operator mistakes, and Texas-specific legal standards — to show how these weaknesses can form the foundation of a strong legal defense.

Key Takeaways

• Improper machine calibration can lead to inflated or completely invalid DWI breath test results.
• Operator errors, such as failing to observe the required period, often render the test legally unreliable.
• Environmental and medical factors can mimic alcohol on a breathalyzer, causing false positives even if no alcohol was consumed.

Can DWI Breath Test Results be Challenged?

Yes. In a DWI case, a breath test result showing a BAC of 0.08% or higher can be the tipping point between a conviction and acquittal. 

Despite their widespread use in law enforcement, breathalyzer devices are not scientifically infallible. In fact, machine calibration issues, operator errors, environmental factors, and physiological conditions can all compromise the accuracy of a breath test.

How DWI Breath Tests Work

DWI breath tests estimate BAC by measuring the amount of alcohol in a person’s breath. These devices, known as breathalyzers or evidential breath test instruments, use infrared spectroscopy or electrochemical fuel cell technology to detect alcohol.

• Preliminary Breath Test (PBT) devices are used during traffic stops for screening.
• Evidential Breath Testing (EBT) machines are used at police stations, and their results are admissible in court.

Popular models include the Intoxilyzer 8000, Intox EC/IR II, and Draeger Alcotest 9510. Each requires precise calibration and trained operation to ensure valid results.

Machine Calibration Problems

What Is Calibration?

Calibration is the process of adjusting a breathalyzer to produce accurate readings by comparing it against a known alcohol standard. Most states require calibration at specific intervals, often monthly or after a set number of uses.

Consequences of Improper Calibration

An improperly calibrated machine can:

• Overestimate BAC levels, leading to false positives
• Fails to detect alcohol at all, giving a false negative
• Trigger "interferent" warnings and fail mid-test

Required Maintenance Records

Law enforcement agencies must maintain calibration logs, which defense attorneys can subpoena. Missing or incomplete logs can render breath test results inadmissible in court.

Example: Massachusetts Breathalyzer Scandal

In 2017, a Massachusetts court threw out 27,000 DWI cases due to unreliable breathalyzer machines that had not been properly calibrated or maintained.

Common Operator Errors

Lack of Training or Certification

Officers must be certified to operate breath test machines and follow strict procedures. If they fail to do so, the results can be challenged.

Typical Operator Mistakes

• Improper observation period (15–20 minutes without eating, burping, or vomiting)
• Failure to detect mouth alcohol, which inflates results
• Not replacing the mouthpiece between tests, risking contamination.
• Skipping system checks or ignoring error codes

Example: Texas Case Thrown Out

In 2022, a Texas DWI case was dismissed after it was revealed that the officer failed to complete the required 15-minute observation period, casting doubt on the breath result.

Environmental and Physiological Interference

Even when the machine is calibrated and the operator is trained, outside factors can still cause faulty readings.

Environmental Factors

• Paint fumes, acetone, or alcohol-based cleaners can be inhaled and skew results.
• Radio frequency interference from police radios may disrupt older machines.
• Temperature changes affect breath sample volume and measurement accuracy.

Physiological Factors

• Gastroesophageal reflux disease (GERD) or acid reflux can cause mouth alcohol.
• People with diabetes can produce acetone, which mimics ethanol on some breathalyzers.
• Ketosis from fasting or ketogenic diets may be misread as alcohol.

According to a study published in the Journal of Analytical Toxicology, ketones and medical conditions can lead to false positive results, especially on older or less sophisticated machines.

Real Case Examples of Inaccurate DWI Breath Tests

Texas-Specific Considerations for DWI Breath Tests

While DWI breath test challenges are possible in every state, Texas law and procedures introduce unique factors that can significantly impact your defense strategy.

Texas Law Requires Strict Breath Test Protocol Compliance

In Texas, breath tests must comply with the standards set by the Texas Department of Public Safety (DPS) under Title 37, Part 1, Chapter 19 of the Texas Administrative Code. These regulations govern:

• Approved breath testing machines (e.g., Intoxilyzer 9000, Intox EC/IR II)
• Mandatory 15-minute observation period
• Routine instrument calibration checks
• Certification of technical supervisors and breath test operators

Failure to comply with any of these protocols may lead to suppression of breath test evidence in court.

Technical Supervisors Play a Key Role

Only certified Technical Supervisors, licensed by the Texas DPS, are allowed to oversee breath testing programs. They are responsible for:

• Verifying machine calibration and maintenance
• Training and certifying operators
• Providing expert testimony in court

If a technical supervisor failed to document proper maintenance or allowed uncertified personnel to conduct tests, the breath test results may be deemed unreliable under Texas law.

Kelly v. State: Texas Courts Allow Breath Test Challenges on Scientific Grounds

Texas courts recognize scientific reliability challenges under Kelly v. State, 824 S.W.2d 568 (Tex. Crim. App. 1992). This means:

• The defense can challenge the underlying science or methodology of a breath test.
• A judge must determine whether the test meets reliability standards before it’s admitted.
• Expert testimony can be used to discredit results from improperly used or maintained machines.

This provides attorneys in Texas with powerful tools to contest flawed breath test evidence.

Visual: Texas DWI Breath Test Procedure Flow

Here’s a simplified flowchart outlining how breath test procedures should work under Texas law:

Recent Texas Case Law Supporting Breath Test Challenges

Texas courts have consistently scrutinized the scientific reliability, procedural compliance, and evidentiary admissibility of breath test results in DWI cases. Below are other key Texas appellate decisions that illustrate how DWI breath test results can be successfully challenged.

1. State v. Esparza, 413 S.W.3d 81 (Tex. Crim. App. 2013)

Issue: Admissibility of breath test refusal evidence

Significance: Although the case focuses on refusal to submit to breath testing, it reaffirmed that DWI prosecutions rely heavily on procedural integrity and evidentiary standards. The court reinforced the importance of proving reliable administration of chemical tests under Kelly.

2. Reyna v. State, 434 S.W.3d 272 (Tex. Crim. App. 2014)

Issue: Right to confront breath test operator

Significance: This case held that under the Confrontation Clause, a defendant has the right to cross-examine the person who conducted or supervised the breath test—not just the person interpreting the data.

Why it matters: If a breath test was administered by someone unavailable or uncertified, or if proper records are not presented in court, the defense may challenge the evidence.

3. State v. McDougald, No. 05-19-01243-CR (Tex. App.—Dallas, 2021)

Issue: Inadequate observation period before breath test

Significance: In this case, the court considered whether failure to conduct the 15-minute observation period required under Texas Admin properly. Code rules affected the admissibility of the breath test result.

Outcome: The breath test was excluded for noncompliance with procedural requirements, further strengthening the argument that strict adherence to DPS protocols is mandatory.

4. Anderson v. State, No. 13-21-00075-CR (Tex. App.—Corpus Christi, 2022)

Issue: Missing calibration records

Significance: The court reviewed a DWI conviction in which the defense raised concerns about incomplete calibration logs for the breathalyzer. The court noted that a failure to maintain or produce maintenance records casts doubt on the reliability of breath test results.

Summary Table: Texas Case Law Challenges to DWI Breath Tests

These cases show that in Texas, DWI breath test evidence is not automatically accepted. It must be supported by strict compliance with scientific standards, administrative code, and constitutional protections.

Legal Defenses Based on Breath Test Errors

If your case hinges on a breath test result, your attorney may raise one or more of these defenses:

• Requesting calibration and maintenance logs
• Reviewing the operator’s certification and training
• Challenging observation period compliance
• Citing physiological or medical conditions
• Requesting an independent forensic toxicology review

These defenses often lead to suppression of the breath test, which can significantly weaken the prosecution’s case.

FAQs

How often do breathalyzers need to be calibrated?

Most states require monthly calibration or after a set number of uses. Some models also require daily accuracy checks.

What happens if a breath test machine isn’t calibrated?

An uncalibrated machine may return unreliable results, which can be deemed inadmissible in court if challenged.

Can medical conditions affect breath test results?

Yes. GERD, diabetes, and ketosis can cause mouth alcohol or acetone production, which may mimic ethanol.

What is the observation period before a breath test?

Typically, 15 to 20 minutes during which the suspect must not eat, drink, burp, or vomit. Skipping this step is a significant procedural error.

Can breath test results be wrong?

Absolutely. Due to machine issues, human error, and external factors, false positives are more common than many realize.

Sources: Michael & Associates research, Texas DWI and DUI Glossary, Journal of Analytical Toxicology, DWI Science Glossary, Google Scholar, Justia, Texas Administrative Code, Texas Department of Public Safety, Texas Tribune, Texas Court of Criminal Appeals. The researchers at Michael & Associates have verified all information.