The Forensics of BAC: Blood vs. Breath
Blood Alcohol Content (BAC) is a measure of the weight of alcohol in a certain volume of blood. While a blood draw is the 'Gold Standard' of accuracy, roadside breathalyzers are the most common tool used by law enforcement. However, these devices do not actually measure blood; they measure 'Deep Lung Air' (alveolar air) and use a fixed mathematical 'Partition Ratio' of 2100:1 to estimate what is in your blood. This estimation assumes that every person's physiology is identical, which is the primary point of failure in many DUI court cases.
Fuel Cell vs. Infrared: How the Tech Fails
Law enforcement typically uses two types of technology. Handheld 'PBT' (Preliminary Breath Test) devices usually use fuel cell sensors, which generate an electrical current when alcohol is oxidized. These are sensitive to temperature and cigarette smoke. Evidentiary station-house machines use Infrared (IR) Spectrometry, which measures how much light of a specific wavelength is absorbed by alcohol molecules in the breath sample.
Premium Benchmarks
Fuel Cell PBT (Roadside)
+/mo
Highly portable but prone to environmental interference and calibration drift.
Infrared Spectrometry (Station)
+/mo
More stable, yet still reliant on the Partition Ratio being accurate for your specific body.
Medical Technicalities: GERD and 'Mouth Alcohol'
One of the most successful ways to challenge a breathalyzer is the 'Mouth Alcohol' defense. If a driver has Gastroesophageal Reflux Disease (GERD) or chronic acid reflux, alcohol from the stomach can be pushed back into the oral cavity. When the driver blows into the machine, it measures this concentrated stomach vapor rather than deep lung air, resulting in a 'false high' BAC reading. Similarly, 'Ketone Breath' caused by diabetes or high-protein diets can sometimes be misidentified as ethanol by older fuel cell machines.
The Post-Stop Legal Roadmap
If you believe a breathalyzer result was inaccurate, the actions you take in the first 24 hours are critical for your defense. Documentation is your strongest weapon when challenging a state's evidence.
01
Request Independent Blood Test
In many states, you have a legal right to an independent blood test at your own expense if you dispute the breath results.
02
Document Medical History
If you have GERD, diabetes, or specific dental work that traps food particles, secure medical records from your doctor immediately.
03
Subpoena Calibration Logs
Work with an attorney to check the device's maintenance history; if it wasn't calibrated within the legal window, results may be suppressed.
The Expert Truth on Alcohol Myths
There is an abundance of misinformation regarding how to 'beat' or 'trick' a breathalyzer. From copper pennies to sucking on batteries, these urban legends have no basis in chemistry or physics.
The Expert Reality: Placing a penny under your tongue does not affect fuel cell or IR sensors. The only thing that lowers your BAC is time. The liver metabolizes alcohol at a constant rate of approximately 0.015% per hour. Coffee, cold showers, and breath mints may hide the smell, but they do not change the alveolar air content measured by the machine.
Conclusion
The 'technicality' in a DUI case isn't about luck; it's about the application of forensic science. By understanding the limitations of breathalyzer technology and the medical factors that can influence BAC readings, drivers can better navigate the legal complexities of a violation. Reinstatement often depends on whether these readings hold up in a court of law.