DWI Breathalyzer Tests: Accuracy, Errors, and How to Challenge Results
Many people assume breathalyzer readings are infallible, but that’s far from the truth. These machines can give inaccurate readings for a variety of reasons, some of which have nothing to do with how much alcohol someone’s actually consumed.
If you’ve been charged with a DWI based on a breath test, it’s important to understand how these devices work and the possible errors that can occur. McDougal Law Firm in Richmond, Texas, can help you understand the details of breath tests so you can build a strong defense and protect your rights.
How Breathalyzers Work in Texas DWI Cases
In Texas, when a driver is suspected of driving while intoxicated, law enforcement may request a breath sample to determine blood alcohol concentration (BAC). The breathalyzer device analyzes the amount of alcohol in a person’s breath and calculates an estimated BAC.
According to the Texas Department of Transportation, if the result is 0.08% or higher, the driver can be arrested and charged with DWI.
However, breathalyzers don’t directly measure the alcohol in your blood—they estimate it by evaluating the alcohol in your breath. This estimation process introduces several opportunities for error, which makes these results vulnerable to legal challenges.
Factors That Affect Breathalyzer Accuracy
Although breathalyzers are widely used in DWI cases, their reliability isn't absolute. Many different factors can interfere with the accuracy of these devices and the readings they produce. Here are a few external conditions and biological variables to consider:
Mouth alcohol residue: Mouthwash, breath sprays, or recent consumption of alcohol (even without being intoxicated) can leave residual alcohol in the mouth that skews the reading.
Medical conditions: Gastroesophageal reflux disease (GERD), diabetes, or certain diets (like ketogenic diets) can affect breath test results.
Body temperature: Elevated body temperature due to illness or environmental factors can raise BAC readings.
Breathing patterns: Shallow breathing may show a lower BAC, while hyperventilation or holding your breath could inflate the result.
Calibration problems: Breathalyzers must be regularly calibrated to maintain accuracy. If they're not, they may deliver faulty readings.
Improper maintenance: Devices that aren’t cleaned or maintained properly can malfunction.
Operator error: If the officer using the device doesn't follow the correct procedure, the results may be unreliable.
As you can see, both human error and environmental factors can lead to inaccurate test results. That’s why it’s so important to question the test itself, not just the number it spits out.
Legal Standards and Breathalyzer Protocols in Texas
Texas law enforcement officers must follow strict guidelines when administering breath tests. These procedures help protect individuals' rights and aim to make the process as fair as possible. However, these protocols aren’t always followed correctly, and even minor deviations can cast doubt on the validity of the results. Common protocol issues include:
Failure to observe before testing: Officers are supposed to observe the subject for at least 15 minutes before administering the breath test. During this time, the individual shouldn’t eat, drink, burp, or vomit—any of which could affect the test.
Improper certification: Officers must be trained and certified to operate a breathalyzer device. If the person administering the test isn’t certified, that’s a major red flag.
Unrecorded maintenance logs: The breathalyzer must be regularly serviced, and those records must be kept. If the logs are missing, the defense may argue the device was unreliable.
If these procedures aren’t followed to the letter, a defense attorney can argue that the breath test results shouldn’t be used in court.
Common Errors That Lead to False Readings
Despite their reputation, breathalyzers are far from foolproof. Several types of errors can lead to readings that are higher or lower than the driver’s actual BAC. Here are a few mistakes that can lead to false readings:
Contaminated air sample: If the subject burps or regurgitates before the test, the machine may read alcohol from the stomach rather than the lungs.
Interference from substances: Items like cough syrups, hand sanitizers, and other alcohol-containing products can affect the test.
Radio frequency interference (RFI): Police radios, cell phones, and other electronic devices can interfere with some breathalyzer models.
Software glitches: Like any other technology, breathalyzers can suffer from software bugs or firmware issues that skew results.
Each of these errors creates an opportunity to challenge the prosecution’s case and cast doubt on the breathalyzer evidence.
Field Sobriety Tests vs. Breath Tests
In many DWI arrests, officers also use field sobriety tests to help determine impairment. These physical and cognitive tasks—such as walking in a straight line or standing on one leg—are used alongside breathalyzer tests, but they're highly subjective. Here are a few differences in reliability and subjectivity you should be aware of:
Field tests are observational: These rely on the officer’s judgment, which is naturally subjective and can be influenced by bias or stress.
Breath tests are technological: While breathalyzers may seem more scientific, they still depend on proper calibration, handling, and biological variables.
Both tests can be challenged: Field tests may be influenced by medical issues, fatigue, or nervousness, while breathalyzers are susceptible to technical and environmental errors.
Understanding how these two types of tests differ can help you and your attorney build a well-rounded defense.
Refusing a Breathalyzer Test in Texas
In Texas, implied consent laws mean that if you're arrested for DWI, you’re considered to have already consented to chemical testing. However, you still have the right to refuse a breathalyzer test, but doing so comes with its own consequences. Here’s what can happen if you refuse the test:
License suspension: Refusing a breathalyzer test can lead to an automatic license suspension for 180 days or more.
Evidence of guilt: Prosecutors may argue that your refusal suggests guilt, and juries may be told about it in court.
No breath sample to challenge: Refusing means there’s no BAC reading to dispute, which can be a double-edged sword.
While refusal can make it harder for the state to prove a specific BAC, it can also result in immediate penalties and be used against you in court. Your attorney can help weigh the pros and cons based on the facts of your case.
When Breath Tests and Blood Tests Don’t Match
There are times when a breathalyzer and a blood test yield very different results. This discrepancy can become a powerful part of your defense, especially if the breathalyzer shows intoxication and the blood test doesn’t, or vice versa. Some reasons for mismatched results can include:
Timing difference: Alcohol levels can rise or fall quickly, depending on when the tests are taken.
Absorption rate: Everyone processes alcohol at a different rate, and peak BAC can occur after driving has ended.
Test sensitivity: Blood tests are more precise than breathalyzers and are less likely to be affected by environmental or physiological factors.
If there's a significant gap between the two results, your attorney can argue that the breathalyzer test isn't reliable enough to convict.
Contact Us Today
A breath test might seem like airtight evidence, but in reality, it’s filled with potential problems. If you’ve been charged with a DWI in Texas based on a breath test, a skilled attorney can fight for a better outcome in your case. We serve clients in Richmond, Texas. Reach out to McDougal Law Firm today to get started with a consultation.
