Contrary to popular opinion, breathalyzers don’t just mechanically or chemically analyze and report the amount of alcohol in a breath sample. The machine is run by an internal computer — a computer which is, of course, controlled by software written by the manufacturer. This software determines everything about the operation of the machine — its setup, capture of breath sample, analysis, and even "interpretation" of the results. For example, the computer will multiply the amount of alcohol it has determined to be in the breath by a factor — usually 2100 — to get the amount in the blood.

This 2100 figure is based upon the partition ratio in the average human; the actual ratio varies widely from one person to another. This variance already lends itself to significant error in results, but what ratio was actually used in the software? Does the software program even comply with the government’s standards for breath analysis?

We don’t know — any more than we know anything else about how this particular machine’s software was designed to analyze and report breath alcohol — unless we have access to the software code. In other words, the amount of alcohol actually in the breath sample is meaningless if the software code causes the machine to analyze and report erroneously. GIGO, as the computer folks say: "Garbage In, Garbage Out". The problem is that manufacturers are unwilling to provide those codes — not even to the police or prosecutors.

Why? Their stock reply is protection of "trade secrets". This is patently ridiculous, of course: Any concerns can be addressed by a court order limiting access to the code to a defense expert witness. In any event, the manufacturer is capable of suing for any unlikely infringements.

The real reason for the secrecy is that manufacturers are afraid of having defects, inaccuracies and/or non-compliance in the code revealed. If a citizen is accused of driving with a blood-alcohol level of .08% of higher, the only real evidence is the machine’s reading. But for years, manufacturers have been successful in keeping those citizens from finding out whether their machines are accurate and reliable. Until recently….

Surprise court ruling threatens to nullify results of DUI tests

Venice, FL. November 4 – In a decision that could throw out the use of alcohol-breath test results in Sarasota County drunken-driving cases, a panel of judges ruled that defendants are entitled to inspect the source code of the breath-testing machine’s software, though the manufacturer has refused to divulge it.

Three Sarasota County judges surprised prosecutors Wednesday when they sided with Venice defense attorney Robert Harrison by giving the state 15 days to produce the machine’s source code for the defense. The catch: the Kentucky-based manufacturer, CMI Inc., has refused to turn over the code — the electronic instructions that drive the machine — calling it a trade secret…

The order, prosecutors say, threatens to nullify breath test results from the Intoxilyzer 5000, which police statewide use to measure whether a driver’s blood-alcohol content exceeds the .08 legal limit. Those results can often be one of the most damning pieces of evidence introduced in a DUI case… Attorneys close to the case expect the state’s attorney to appeal. In the meantime, police will continue to the use the test despite the deadlock over source code….

The ruling isn’t the first of its kind in Florida. Last November, judges in Seminole and Orange counties decided to exclude Intoxilyzer 5000 breath-test results from hundreds of cases. But judges in two other Florida counties have ruled otherwise, upholding prosecutors’ arguments that they can’t turn over something they do not possess and that the code itself is immaterial to the DUI cases. CMI refused to comment Thursday.

"Full information should include the software that runs the instrument," reads the order, signed by county judges David Denkin, Kimberly Bonner and Judy Goldman. "Unless the defense can see how the breathalyzer works and verify it is an approved machine, it remains …. nothing more than a ‘mystical machine’ used to establish an accused’s guilt."

The judges ruled that a look at the source code was material to the case, based on photographic evidence that showed visible differences in the arrangement and number of erasable and programmable memory chips inside Intoxylizers now in use throughout Sarasota County. An expert witness testified that without the source code, he would be unable to determine whether any changes or modifications had occurred.

"Unless the defense can see how the breathalyzer works and verify it is an approved machine, it remains …. nothing more than a ‘mystical machine’ used to establish an accused’s guilt." Finally.