Most states have two criminal charges relevant to "drunk driving". The first is the original law, making it a crime to drive under the influence of alcohol or drugs — also known as "DUI". In more recent years, and under pressure from the federal government, all 50 states passed the so-called "per se statute", making it a crime to drive with a blood alcohol concentration (BAC) of .08% or more — regardless of whether the driver was under the influence of alcohol or not. In most states, both crimes can — and usually are — charged (assuming there was a blood alcohol test).
With the first offense, the prosecution can offer various kinds of evidence: erratic driving, flushed face, bloodshot eyes, slurred speech, poor balance and/or coordination, failing the "field sobriety tests", etc. In addition, if the blood alcohol test indicated a BAC level of .08% or more, the judge would instruct the jury that the defendant was rebutably presumed to be under the influence — that is, he was presumed to be guilty, but could offer contradicting evidence of his own.
With the second offense, the blood alcohol level is the crime: regardless of intoxication or sobriety, it is a criminal offense to have .08% or more while driving. Unless the defendant could prove that the breathalyzer was unreliable in some way — incorrectly maintained, calibrated or operated or otherwise defective — the crime was proven.
In other words, the machine is judge, jury and executioner.
So….just how accurate are these so-called breathalyzers?
Not very. These machines are susceptible to hundreds of different problems. To give you some idea, a good survey of the more common potential defects inherent in any breath alcohol test can be found on the website of my DUI defense firm,The Law Offices of Lawrence Taylor. The 3-page discussion is located in the "Police Evidence" section, under the heading DUI Breathalyzer Accuracy.
The problem is that these defects can only be revealed through extensive investigation by an experienced DUI defense attorney, usually through the legal procedure known as discovery. This is the use of subpoenas, motions in court, and other proceedings involving, among other things, the testing police officer’s operation, the individual machine’s data, law enforcement crime lab procedures and calibration records, machine usage logs, and even video cameras in the testing room.
In other words, it takes an experienced DUI attorney in this complex field who is prepared to devote the time and resources necessary to reveal the flaws. And such attorneys don’t come cheap. So if you suddenly need a DUI attorney, ask yourself: If I needed heart surgery, would I try to find the cheapest surgeon?