Breathalyzer Tests: How Often Are Breathalyzers Wrong?

Breathalyzer devices are commonly used across Virginia to evaluate a driver’s blood alcohol concentration (BAC). Although these tools are considered reliable, they are not infallible. But just how often are breathalyzers wrong? At Flusche & Fitzgerald, we understand how daunting it can be to face DUI charges based on potentially flawed breathalyzer results. Our mission is to help you navigate these challenges with confidence and clarity.

Examining Breathalyzer Accuracy

Breathalyzer readings are generally accurate when administered correctly. However, studies suggest that errors occur in a significant percentage of cases, highlighting why challenging results in Virginia DUI cases is often warranted.

Reasons for potential inaccuracies include:

1. Calibration Issues. These devices require regular calibration to maintain reliability. If not properly maintained, they may deliver flawed results.
2. Procedural Errors. Law enforcement must follow specific protocols when using a breathalyzer. Deviations from these procedures can affect the validity of the results.
3. Environmental Influences. External factors, such as temperature variations or chemical fumes, can interfere with the device’s performance.

Understanding these issues is crucial. If any of these factors apply to your situation, they could provide grounds to challenge the test’s results.

Ultimately, can breathalyzers be wrong? Yes, they can, depending on many different factors that may be at play.

How Does Virginia’s Evidential Breath Test Work?

A preliminary breath test (PBT), sometimes called a portable breath test, is a handheld device that an officer may use during a traffic stop to determine whether there is probable cause to arrest for DUI. Under Virginia law, you may refuse the roadside PBT.

Yet an officer may conclude that they have probable cause to arrest you, even if you refuse. An arrest changes your options.

Evidential Testing After an Arrest

If an officer arrests you for suspected DUI, police generally use an Intox EC/IR II machine to perform an evidential breath test—a test whose result prosecutors may introduce in court. Virginia’s implied consent law states that, by driving on a public highway, Virginia drivers agree to provide a blood or breath sample after arrest for DUI. At that point, refusal becomes a civil offense.

The Virginia Department of Forensic Science (DFS) certifies and maintains the Intox EC/IR II instruments used throughout Virginia and licenses the officers who operate them. The machine uses infrared analysis to monitor the sample and check for alcohol remaining in the mouth. The machine then sends part of the sample to an electrochemical fuel cell, which produces an electric current that the machine uses to calculate the amount of alcohol in the breath.

The 20-Minute Observation Period

Before the test begins, the officer must observe you for at least 20 minutes. During that period, you cannot eat, drink, smoke, vomit, regurgitate, or ingest fluids. If you do, the officer must begin another 20-minute observation period.

This waiting period gives alcohol remaining in the mouth time to clear.

Machine Checks and Reference Samples

After the observation period, the operator enters identifying information. The machine then performs diagnostic checks and analyzes the surrounding air for alcohol or other substances.

Next, the Intox EC/IR II analyzes a dry gas standard containing a known amount of alcohol and compares its reading to that of the surrounding air. It then analyzes the surrounding air again before requesting your first breath sample.

DFS also uses simulator solutions during laboratory testing. A simulator heats a liquid containing a known amount of alcohol, producing alcohol vapor. DFS analyzes the vapor to check whether an instrument is properly calibrated.

Breath Samples and the Certificate of Analysis

You must provide at least two breath samples. Between samples, the machine clears its testing system, analyzes the surrounding air again, and imposes a two-minute waiting period. If the first two samples differ by 0.02 grams per 210 liters or more, the machine requests a third sample.

When two samples fall within the required range, the machine reports the lower result. The Intox EC/IR II prints a Certificate of Analysis that identifies the person tested, the operator, the machine, and the test result.

What Can Affect an Intox EC/IR II Result?

The Intox EC/IR II contains safeguards intended to avoid some testing problems, but those safeguards do not resolve every question about a result. Your attorney can review whether the officer followed the required procedure, whether the machine accepted each check, and whether differences in your body could have affected the relationship between your breath and blood alcohol concentrations.

Testing and Operator Errors

A DFS-licensed operator must administer the test according to Virginia procedures. An attorney may check several specific parts of that process, including:

• An incomplete observation period,
• Incorrect identifying information,
• A machine message that required further action, and
• An incomplete testing sequence.

An attorney can use the Certificate of Analysis, test data, officer’s worksheet, video, and DFS records to determine what the officer and machine actually did.

Machine and Environmental Issues

Machine and environmental issues fall into two broad categories: the instrument’s reliability over time and the conditions surrounding a particular test. DFS certification, maintenance, and repair records document the machine’s history, while the test data show how it operated when police tested you.

The Intox EC/IR II uses internal checks to identify problems involving the machine, its surroundings, or the testing sequence. It should stop rather than report a result when it detects certain problems. An attorney can review the machine’s records and the individual test data together to determine whether those safeguards support the reported result or leave an accuracy issue unresolved.

Police radios, cell phones, and other transmitting devices can produce radio frequency interference (RFI). If the machine detects strong interference, it should abort the test and report “AMBIENT/RFI DETECTED,” but a miscalibrated machine may not operate correctly.

Differences Between People

People vary, so there is no single universal false-positive rate for breathalyzers. Breath testing relies on an assumed relationship between alcohol in a person’s breath and alcohol in the person’s blood. Analysis often assumes a standard breath-to-blood partition ratio of 2,100:1, meaning that evaluators treat 2,100 milliliters of breath as containing the same amount of alcohol as 1 milliliter of blood.

Actual ratios vary among individuals and may change with body temperature and the timing of the test. And hematocrit, the percentage of blood made up of red blood cells, can also affect the relationship between alcohol in the breath, the liquid portion of the blood, and whole blood.

What Besides Alcohol Can Set Off a Breathalyzer?

Breathalyzers are designed to detect ethanol—the type of alcohol found in beverages. However, other substances can cause inaccurate readings, including:

• Personal hygiene products. Mouthwashes or sprays containing alcohol may linger in the mouth, affecting results.
• Medications. Certain over-the-counter remedies, including cough syrups, contain alcohol that can influence tests.
• Medical conditions. Diabetic individuals or those following low-carb diets can produce acetone, which mimics ethanol in readings.

Gastroesophageal reflux disease (GERD) can cause stomach contents to flow into the esophagus or mouth. If the stomach contains recently consumed alcohol, reflux could introduce that alcohol into a breath sample.

The Intox EC/IR II is designed to distinguish interfering chemicals from ethanol. If it detects acetone or another possible interference, it should stop the test and print an “INTERFERENT DETECTED” message.

Knowing these triggers can help you identify potential inaccuracies in your own case. Always inform your attorney about any relevant factors that could have affected the test results.

Foods That Cause False Positive Breathalyzer Results

Surprisingly, everyday foods and beverages may also lead to false positives, including:

• Fermented products. Items such as bread or ripe fruit may contain trace alcohol from fermentation.
• Non-Alcoholic drinks. Even beverages labeled “non-alcoholic” often contain small quantities of alcohol.
• Energy drinks. Ingredients in these beverages may mimic alcohol when analyzed by a breathalyzer.

If you suspect your BAC reading was impacted by food or drink, providing this information to your legal team is essential for building your defense.

Can Breathalyzers Produce False Negatives?

A false negative from a breathalyzer is less frequent than a false positive, but can occur. These situations arise when the device fails to detect alcohol despite its presence. Factors contributing to false negatives include:

• Incorrect use. Errors during administration may lead to inaccurate readings.
• Residual alcohol dilution. Consuming water or certain substances may lower detectable alcohol levels.
• Testing timing. BAC readings can fluctuate depending on how long it has been since alcohol consumption.

The biggest issue we see these days with zeroes on the breathalyzer is that the police then simply assume you must be on drugs. That often escalates the situation into a demand and/or search warrant for your blood.

Steps to Take If You Question a Breathalyzer’s Accuracy

Inaccurate breathalyzers are why we recommend that you should NEVER consent to a preliminary/portable breath test in Virginia. That handheld test is always optional, and if it detects any alcohol, that alone can be used as a reason to arrest you.

If you believe your breathalyzer result was inaccurate, consider taking these steps:

1. Document key details. Record what you ate, drank, or any medications you used before the test. Environmental conditions at the time of testing can also be relevant.
2. Seek legal advice. An experienced attorney can analyze the facts of your case and challenge unreliable evidence in court.

Promptly taking these steps ensures your case has the strongest possible foundation. Accurate documentation and timely legal intervention can significantly impact the outcome.

How Flusche & Fitzgerald Can Help

At Flusche & Fitzgerald, we focus exclusively on traffic-related cases, including DUI charges. Our streamlined approach minimizes your stress while ensuring every detail of your case is addressed. From improper calibration to procedural errors, we scrutinize every aspect of your breathalyzer test.

Our attorneys have years of experience navigating Virginia’s courts and maintaining professional relationships with local officers, prosecutors, and judges. These connections, coupled with our focused practice, allow us to achieve the best possible outcomes for our clients.

If you’re facing a DUI charge and believe a breathalyzer test was wrong, let us be your advocates. Contact Flusche & Fitzgerald today for a consultation. Together, we can work toward safeguarding your future and ensuring your case receives the care and expertise it deserves.

Frequently Asked Questions (FAQs)

What Is the 20-Minute Observation Period and What Happens If Police Skip It?

Virginia requires an officer to observe you for at least 20 minutes before an evidential breath test. Eating, drinking, smoking, vomiting, or regurgitating restarts the period. If police skip it, you may be able to challenge the results of the test.

Can GERD or Acid Reflux Cause a False Positive on a Virginia Breathalyzer?

GERD can move stomach contents containing recently consumed alcohol into the mouth. The observation period and the Intox EC/IR II’s mouth-alcohol detection reduce that risk, but do not always eliminate it, depending on operation and maintenance.

What Is the Partition Ratio and Why Does It Make Breathalyzer Results Unreliable for Some People?

The 2100:1 partition ratio assumes a fixed relationship between alcohol in breath and alcohol in blood. Actual ratios vary, so a breath result may suggest a higher or lower blood concentration than a blood test would show.

Does the Preliminary Roadside Breath Test Have the Same Legal Weight as the Station Machine in Virginia?

No. A roadside PBT helps an officer decide whether to make an arrest, but the Commonwealth cannot use it to prove DUI. The Intox EC/IR II produces the post-arrest evidential result that prosecutors may introduce in court. Virginia also permits refusal of the PBT but not the station machine.

Can Medications Like Albuterol or Cough Syrup Actually Fail a Breathalyzer Even If You Haven’t Been Drinking?

Some inhalers and cough syrups contain ethanol that may temporarily remain in the mouth or airway and can trigger false positives.

What Margin of Error Does Virginia Officially Acknowledge for the Intox EC/IR II?

Virginia does not recognize one margin of error. DFS separately evaluates certification accuracy, the dry gas check, agreement between breath samples, and measurement uncertainty.

Legal References Used to Inform This Page

To ensure the accuracy and clarity of this page, we referenced official legal and other resources during the content development process:

• Preliminary analysis of breath to determine alcoholic content of blood, Va. Code Ann. § 18.2-267 (2026).
• Implied consent to post-arrest testing to determine drug or alcohol content of blood, Va. Code Ann. § 18.2-268.2 (2026).
• Virginia Department of Forensic Science, Breath Alcohol.