Texas employs the Intoxilyzer 5000 is used for DWI Breath Alcohol Testing. The Operator’s Manual for this machine is available online here. I know you don’t want to read this manual so let me share some points of interest.
1. The Intoxilyzer Does Not Measure Alcohol
Really. It measures the decrease of energy in a small tube. From the manual-
When alcohol is introduced into the sample chamber, by either the test subject or the reference sample device… the amount of infrared energy reaching the photodetector will decrease. The decrease in the infrared energy striking the photodetector is directly proportional to the increase in the alcohol concentration in the sample chamber. The breath alcohol concentration is determined by the difference between the zero reference point and the breath sample measurement.
The computer then uses a secret formula to convert this into a BAC score. No one knows the formula that is employed.
2. The Accuracy Has Not Improved Since 1980
The machine uses the same chip set it used in 1980. In 30 years the have not managed to improve accuracy. From the manual
In 1980 the Intoxilyzer 4011-A® began use in Texas and in 1988 the Intoxilyzer 5000® was introduced. The Intoxilyzer 5000 is the standard evidentiary breath alcohol testing instrument for law enforcement and is also widely used in industry. The instrument utilizes infrared analysis,while the Breathalyzer uses wet chemical analysis. The biggest difference between the instruments as they have developed relates not to their accuracy and precision or to their method of analysis, but to their automation and ease of operation.
To compare, in 1980 the most advanced video game was Space Invaders. We’ve made a little progress in technology since then.
3. The Machine Is Never Calibrated On Humans.
The machine that is used to convict thousands annually is never calibrated on humans. A reference sample simulator provides a mix of air and alcohol into the machine.