Seven Secrets of the Intoxilyzer

Not all technology is perfect.  In fact none of it is.  Here are a few facts about the Intoxilyzer 8000.

The Seven Secrets of the Intoxilyzer

  1. The Intoxilyzer 8000 is the official breath test instrument of the State of Florida. The police will tell you that it is "tried and true." However, in the computer age, "tried and true" translates into "obsolete." The Intoxilyzer 8000 is based upon the Zilog Z-80 microprocessor. This same chip was the brains of the TandyTRS-80, which was the hit of the home computer 1977!
  2. When the Intoxilyzer is calibrated, if the temperature of the testing solution is off by as little as one-fifth of one degree (.20), the calibration is not considered accurate. Human body temperatures may vary as much as three full degrees-- depending on health, physical activity or even the hour of the day! If you have a slight fever and your body temperature is elevated by only 1 degree Centigrade (1.8 degrees Fahrenheit), your apparent blood alcohol will be artificially inflated by approximately seven percent. (Isn't it interesting how these errors always work against you and never for you?)
  3. The underlying physical principle of the Intoxilyzer is known as "Henry's Law," which states that the concentration of a volatile chemical in vapor above a solution is proportional to the concentration of the chemical in the solution. This is true in the laboratory, but in humans, the proportions can vary by as much as 50%. This means that the Intoxilyzer can overstate your blood alcohol by as much as 50%! As Drs. Stefan Rose and Kenneth Furton have written, "Henry's Law does not apply in the lungs. In order for Henry's Law to apply, three conditions must be met. One, the solution must be in a closed system, like a sealed bottle. The lungs are open, not closed. Two, the solution must be kept at a known, constant temperature. The lung temperature is never known, and the temperature is always changing. And three, the pressure must be kept constant. The lungs are always changing pressure, decreasing pressure to inhale and increasing pressure to exhale. Without all three conditions present, it is not possible for equilibrium to occur, and Henry's Law does not apply."
  4. The Intoxilyzer 8000 operates on a principle known as the "Lambert-Beer Law," which states that the amount of infrared light absorbed by your breath is proportional to the amount of alcohol in the sample. Think of it like the way in which fog will block your car's headlights on a damp night. In short, the more alcohol there is, the less infrared light that gets through the chamber to the detector. However, there are other compounds, called "interferents," which can also block the infrared. And the Intoxilyzer cannot reliably tell them all apart!!
  5. Three or four deep breaths before blowing into the Intoxilyzer will cool your lungs and fill them with fresh air. This sort of hyperventilation may lower your breath alcohol by as much as 55%, without violating the protocols of the test. For more information, see our article on the 3/2 Rule.
  6. The protocol for the Intoxilyzer 8000 in Florida requires only that you blow 1.1 liters of breath. The average adult has a "vital capacity" (the amount he or she can forcibly exhale in one breath) of between three and four liters. The police will urge you to keep blowing your entire breath into the machine. However, such a long breath will artificially increase the apparent amount of alcohol in your breath by skewing the sample toward your "deep lung air," where the alcohol is more highly concentrated. If you only blow half of your breath, you will give an adequate sample, which will be up to 30% less than the sample that the police want you to give.
  7. The Intoxilyzer 8000 measures how much breath you provide by something called a 'pressure transducer.' Instead of directly measuring the volume of your breath by a pressure switch, like the old Intoxilyzer 5000 did, the 8000 indirectly measures breath. Not only is it needlessly complicated, it simply doesn't work! The flow sensor systems in Florida's Intoxilyzer 8000's are so unreliable that FDLE ordered that police STOP KEEPING RECORDS of the system in monthly checks. In 2011, a system-wide check showed that 40% of the machines in Florida couldn't accurately measure breath volume! And on a machine whose pressure transducer was not properly calibrated, the machine was three to five times more likely to deliver an alcohol reading over .25. Sad.

Board Certification in DUI Defense


Tom Hudson passed the National Board Certification Examination (written and oral) in Honolulu in 2008, and was recertified in 2013 and 2018. He was one of the first 50 lawyers granted national board certification in DUI Defense, and is nationally recognized as an authority in DUI law.

Why We're Different

Board Certification as a DUI Specialist by the National College for DUI Defense. Formal NHTSA Certification as an Instructor of the Standardized Field Sobriety Tests given by police in DUI cases. Formal training as a NHTSA Drug Recognition Evaluator. ("Drug Evaluation & Classification") Formal training to operate the Intoxilyzer 8000, Florida's official breath test instrument. Extensive experience in teaching other attorneys how to handle DUI cases. Hundreds of jury trials both as defense lawyer and as prosecutor.