April 8, 2026
Facing a DWI charge in Houston or surrounding areas of Harris, Montgomery, Fort Bend, or Galveston County can be overwhelming. Many people assume that if a breathalyzer or blood test shows they were over the legal limit, their case is hopeless. But what if the science is wrong? Toxicology testing errors – from calibration mistakes to discovery violations to hidden source code flaws – have led to wrongful DWI charges and even invalidation of thousands of test results across the country. This means that a faulty test does not have to ruin your life. In fact, challenging the evidence with the help of an experienced Houston DWI lawyer could be the key to beating your charges.
In Texas, the law is clear about what constitutes “intoxication.” Under Texas DWI laws, a driver is considered intoxicated if they lose the normal use of mental or physical faculties due to alcohol or drugs, or if their blood alcohol concentration (BAC) is 0.08% or higher (see Texas Penal Code §49.01 and §49.04). However, those BAC results are only as reliable as the science and machines behind them. Below, we explore how toxicology testing errors can undermine DWI evidence – and what that means for your case in Houston.
Calibration Mistakes Can Wrongly Inflate BAC Results
Calibration is the backbone of accurate toxicology testing. Breathalyzers and lab instruments must be properly calibrated (i.e. adjusted and checked against known standards) to produce trustworthy readings. If calibration protocols are not followed to the letter, the results can be wildly inaccurate. Calibration mistakes have caused some breath test machines to read artificially high BAC levels – meaning sober or below-limit drivers were flagged as legally intoxicated when they were not.
Real-world examples underscore the danger of calibration errors:
- In Washington D.C., police discovered in 2010 that their breath alcohol analyzers had been mis-calibrated by 20–40% too high for 14 years. A new supervisor found that the reference solution used for calibration was prepared incorrectly, causing roughly 2,500 breath tests to be called into question. This kind of systemic error potentially resulted in numerous wrongful DWI arrests before it was finally caught.
- In New Jersey, a state police sergeant’s failure to properly calibrate Alcotest breathalyzer devices between 2008 and 2016 led to a forensic disaster. The New Jersey Supreme Court in State v. Cassidy ultimately threw out over 20,000 breath test results across several counties. Investigations revealed the coordinator hadn’t used a required calibrated thermometer for the simulator solutions, casting doubt on every DWI conviction that relied on those machines. Many people spent time in jail or paid fines due to what turned out to be faulty test data, and the court ruled those results could not be considered reliable.
- In Pennsylvania, courts halted all DWI breath prosecutions for a time after it came to light that breath test machines weren’t properly calibrated for high BAC levels. In Commonwealth v. Schildt (2012), a judge excluded a breath test reading of 0.21% because the machine’s calibration curve only went up to 0.15%. Since the defendant’s result exceeded the calibrated range, it was deemed unreliable, forcing authorities to fix procedures before cases could resume.
- Even forensic labs can make calibration blunders. In 2021, the Maryland State Police forensic lab was cited for using an inappropriate single-point calibration method for blood alcohol testing – a practice it had been following since 2011. Proper standards call for a multi-point calibration curve spanning the relevant concentration range, not a single data point. Shockingly, the lab passed multiple audits despite this error. This reveals how easily scientific oversight can fail, producing questionable BAC results for years before anyone notices.
These examples show that calibration mistakes are not just technicalities – they strike at the heart of the prosecution’s evidence. If a breathalyzer or lab device in your case was mis-calibrated or maintained improperly, the BAC number being used against you could be flat-out wrong. An experienced attorney can obtain the device’s calibration logs, maintenance records, and even expert testimony to challenge an unreliable test. In Texas DWI cases, the burden is on the state to prove your BAC accurately exceeded the limit (0.08%). If the machine wasn’t in perfect working order, your lawyer can argue the results should be thrown out.
Discovery Violations: When Crucial DWI Evidence Is Withheld
Discovery is the legal process by which the defense is entitled to access the evidence and information the prosecution (and their forensic labs) will use in court. Unfortunately, some agencies have a history of discovery violations – essentially hiding or failing to disclose evidence that could help the defense. In DWI cases, discovery violations often involve withholding technical data about how tests were conducted or any problems that occurred. This lack of transparency can lead to wrongful convictions, and courts do not take it lightly when authorities violate their duty to disclose exculpatory evidence.
One of the most egregious examples comes from Massachusetts. Defense attorneys there suspected that the Office of Alcohol Testing (OAT) was concealing problems with breathalyzer devices. A 2017 investigation confirmed their fears: the state lab had deliberately withheld worksheets of failed breath test calibrations and even had an unofficial policy to not turn over certain documents to defendants. This cover-up lasted for years. In 2023, Massachusetts’ highest court concluded that OAT’s “disturbing pattern” of intentionally hiding exculpatory evidence since at least 2011 violated due process for tens of thousands of drivers. The Supreme Judicial Court ruled that approximately 27,000 DWI cases were tainted and gave those defendants the right to new trials or withdrawal of guilty pleas. In other words, nearly eight years’ worth of breath test results (from a specific device model) were deemed unreliable and inadmissible because the government failed to play by the rules.
Texas has its own discovery obligations under Brady v. Maryland, requiring prosecutors to hand over any evidence that could be favorable to the defense. If a lab or officer in your Houston DWI case knew of a potential issue – say, a malfunctioning vial in a blood test or prior failed accuracy checks on a breathalyzer – and did not disclose it, that is a serious violation of your rights. Courts have called out such behavior as egregious misconduct. For instance, legal experts note that presenting a DWI test result as infallibly accurate without revealing its margin of error or problems is misleading – some even argue it amounts to a Brady violation to pretend a scientific result is 100% certain when it’s not.
Other cases highlight why full discovery is so critical. In State v. Cruz-Romero, an Idaho man’s breath test showed 0.097% BAC, just over the limit. It later emerged that the machine had failed multiple calibration checks around the time of his test. Prosecutors initially succeeded in blocking this information, and he pled guilty. But on appeal, the court ruled the evidence of those failed calibration checks was relevant and should not have been excluded – even without a defense expert to explain it. Hiding such facts unfairly handicaps the defense.
The takeaway is that you have the right to know exactly how your DWI evidence was generated. A skilled attorney will demand maintenance records, lab batch reports, chromatograms, calibration logs, software printouts – everything. If the police or lab withhold anything or if they’ve lost critical evidence (like sample chain-of-custody paperwork or video of your breath test), a Houston DWI attorney can file motions to exclude the test or even dismiss the case for discovery violations. The Napier Law Firm understands these tactics and will hold the state accountable to provide every piece of discoverable information. We leave no stone unturned because sometimes what’s hiding under that stone can blow apart the prosecution’s case.
Source Code Flaws in Breathalyzers: Hidden Software Errors That Matter
Modern breath alcohol tests are essentially computers analyzing your breath sample. And like any computer, they run on software – source code written by humans. If there’s a bug in the code, the device can malfunction or give false readings. Unlike a visibly broken part, software bugs are invisible and can quietly taint thousands of tests before anyone finds out. Unfortunately, manufacturers have historically treated breathalyzer source code as a trade secret, fighting to prevent defense teams from examining it. But when the code has been reviewed (usually after hard-fought legal battles), serious flaws have been uncovered.
One dramatic example occurred in Minnesota with the Intoxilyzer 5000EN (a breathalyzer previously used in many states, including Texas in past years). Around 2011, during a wave of source code litigation, a judge found that the Intoxilyzer’s programming had a significant error: if a person blew just slightly too hard at the start of the test, the machine would improperly throw out the sample and register it as a refusal. In other words, drivers who did provide an adequate breath sample were falsely accused of refusing the test due to a software glitch! Incredibly, evidence showed the state crime lab had received a patch to fix this bug back in 2007 – but they never installed it because they “did not want to draw attention” to the issue. Instead, authorities let the flawed code be used for years, and officers simply assumed anyone flagged as “refused” was non-compliant, when in reality some had complied perfectly. This kind of flaw directly leads to wrongful charges (a refusal can carry the same or worse penalties than a DWI in Texas). It only came to light because persistent defense attorneys forced a review of the source code.
Another high-profile source code case was State v. Chun in New Jersey. There, the state Supreme Court allowed independent computer experts to examine the Alcotest 7110 breathalyzer’s code. The experts found thousands of programming errors and outdated coding practices that did not meet modern quality standards. The court concluded that, despite these errors, the device could still be used if specific software corrections were made and documented. The Chun case is important because it proved that breathalyzer software is far from pristine – even widely used, state-approved machines had sloppy code under the hood. It set a precedent for transparency: if we trust these devices to decide people’s guilt or innocence, their inner workings must withstand scrutiny.
Software issues continue to emerge as machines become more advanced. For instance, Washington State’s forensic lab found a bug in the Draeger Alcotest 9510 (the successor to the 7110) that sometimes caused the device to reject valid breath samples erroneously. Upon review of 81,000 breath tests, at least a handful of instances were identified where the machine should have accepted the results but didn’t. Those defendants could have been wrongly deemed to have an incomplete or failed test due to a silent software hiccup.
What do these technical tales mean for someone charged with DWI in Houston? They illustrate that breath test results are not infallible. Texas currently uses the Intoxilyzer 9000 for breath tests – a device that, like those above, has a complex software brain. If there are any known issues or updates to its software, a diligent lawyer will find out. The Napier Law Firm can leverage expert forensic consultants to review device source code (if obtainable) or at least examine the data the machine produces for anomalies. We stay updated on national developments and legal standards, because a flaw discovered in one state (e.g. a tolerance range bug in the Alcotest 9510 software) might apply to the same model used in Texas. Our team will aggressively pursue technical defenses if there’s any indication your test result was affected by a software or programming error. Remember, a machine’s readout is only as good as the code and calibration behind it – and we can expose when something doesn’t add up.
Why Toxicology Errors Matter to Your DWI Case in Texas
You might be thinking, “These examples are from other states – does that really apply to my DWI case in Texas?” The answer is yes. The science of breath and blood testing is the same everywhere, and errors have indeed occurred in Texas cases. Houston and surrounding counties use the same kinds of breathalyzers and blood analysis techniques seen in these examples. In fact, large agencies like the Texas Department of Public Safety (DPS) manage breath testing programs statewide, and they rely on the integrity of their labs and machines. If something goes wrong – a negligent lab technician, a broken calibration tool, a software bug – it could easily impact hundreds of cases before detection.
Moreover, Texas courts have shown they will exclude evidence or even overturn convictions if the scientific foundation is faulty. For instance, Texas follows Daubert standards for scientific evidence, requiring that techniques like breath tests have a reliable basis. If your attorney can demonstrate a serious flaw in how your BAC was determined, a judge can rule the evidence unreliable and inadmissible. Without BAC evidence, many DWI cases fall apart or become much easier to fight (the prosecution may have to rely only on officer observations, which are often subjective).
Consider also that Texas’s Administrative License Revocation (ALR) process (which can suspend your license for a failed or refused test) can be contested on similar grounds. If the breathalyzer wasn’t maintained to DPS specifications, that can be argued at your ALR hearing to save your license. The bottom line is that challenging toxicology errors is a core part of DWI defense. It can lead to reduced charges, case dismissal, or acquittal. It can also provide leverage to negotiate a better outcome, since a shaky test result is a huge weakness in the state’s case.
At The Napier Law Firm, we work with clients in Harris County, Montgomery County, Fort Bend County, and Galveston County who are often surprised to learn how much scientific evidence can be questioned. Our job is to raise that reasonable doubt. We have seen first-hand that police and labs make mistakes – machines break, human operators err, and sometimes officials do not follow the strict protocols that Texas law and national standards require for DWI testing. When we take on your case, we will immediately begin a thorough investigation into the technical details. This includes requesting equipment maintenance logs, lab results and bench notes, video or printouts from the breath test, training records of the officer or technician, and more. We may consult former lab analysts or forensic toxicologists to identify any irregularities. If there’s a discrepancy or red flag, we will use it to challenge the validity of the prosecution’s evidence.
Fighting Back with a Houston DWI Attorney Who Understands Science
Toxicology errors can be complex, but as a defendant you don’t need to be a scientist – you just need a lawyer who works with the right experts and knows how to use these issues to your advantage. George Napier, the founder of The Napier Law Firm, has undergone the same DWI investigation training that law enforcement officers do, giving him insight into how the state builds its case and where its weaknesses lie. Our legal team stays up-to-date on developments in forensic science and DWI case law. We know, for example, that failing to disclose a machine’s failed quality-checks or not providing the uncertainty of a blood test result can deprive you of a fair trial – and we’ll fight to ensure that doesn’t happen in your case.
If you suspect that a breathalyzer error, lab mistake, or police oversight played a role in your DWI arrest, don’t leave it to chance. This isn’t a defense you typically win by yourself; it requires digging into the evidence with a fine-tooth comb. Our firm has the resources and determination to do just that. We treat every DWI case as unique – because it is. Maybe the police station’s breath machine wasn’t inspected on schedule, maybe the blood vial’s seal was broken, or maybe the officer skipped a required 15-minute observation period before your breath test. These details can make the difference between a conviction and a dismissal.
Contact The Napier Law Firm today to discuss how we can help. As a dedicated Houston DWI attorney, George Napier has successfully defended clients throughout the Greater Houston area – including Houston, Conroe, Richmond, Galveston and beyond – by exposing flaws in the prosecution’s evidence. We offer a free consultation, and we’re available 24/7 to answer your questions.
Sources:
- Texas Penal Code §49.01(2)(A)-(B) – Legal definition of “intoxicated” (normal use of faculties lost or BAC ≥0.08%).
- State v. Cassidy, 235 N.J. 482 (2018) – NJ Supreme Court case invalidating 20,667 breath tests due to improper calibration checks.
- Olson & Ramsay (2025) – Compilation of toxicology errors (Forensic Sci. Int. Synergy) – D.C. breathalyzer miscalibration 20–40% high for 14 years; Maryland single-point blood test calibration error (2011–2021); Pennsylvania Comm. v. Schildt halting high-BAC breath cases due to calibration range issue.
- Olson & Ramsay (2025) – Discovery violations in DWI testing – Massachusetts OAT withholding of failed calibration records (2011–2017) and SJC ruling allowing 27,000 cases to be retried or dismissed for “egregious” misconduct; State v. Cruz-Romero, 160 Idaho 565 (2016) – improper exclusion of evidence on breathalyzer calibration failures overturned on appeal; Expert commentary deeming lack of uncertainty disclosure a Brady violation.
- Olson & Ramsay (2025) – Source code flaws in breath alcohol testing – Minnesota Intoxilyzer 5000EN software bug causing false refusals (patch withheld); State v. Chun, 194 N.J. 54 (2008) – review finding thousands of errors in Alcotest 7110 source code; Washington State Alcotest 9510 software tolerance bug (2021) causing rejection of valid tests.
- Aaron Olson, Charles Ramsay (Dec. 2023) – The Misleading Presentation of DWI Test Results: A Call for Better Science – interview discussing the importance of disclosing uncertainty and interference issues in DWI chemical tests