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As with the odor of alcohol on the breath, few police reports will fail to include an observation by the arresting officer that the arrestee exhibited “slurred speech”.  The officer fully expects to hear slurred speech in a person he suspects is intoxicated, particularly after smelling alcohol on the breath, and it is a psychological fact that we tend to “hear” what we expect to hear. And hearing it supplies the officer with corroboration of his suspicions.

Even assuming the honesty of the officer that the defendant’s speech was slurred, there is little evidence that this is symptomatic of intoxication. Impairment of speech is, for example, a common — and sober — reaction to the stress, fear and nervousness that a police investigation would be expected to engender.  Fatigue is another well-known cause.

Skeptical?  Consider the following excerpt from Discover magazine (Saunders, “News of Science, Medicine and Technology: Straight Talk”, 21(1) Discover (Oct. 2000).

Bartenders, police officers and hospital workers routinely identify drunks by their slurred speech. Several investigative groups judged the captain of the Exxon Valdez oil tanker to be intoxicated based solely on the sound of his voice in his radio transmissions. But a team led by Harry Holien, a phonetician at the University of Florida, has found that even self-proclaimed experts are pretty bad at estimating people’s alcohol levels by the way they talk.

Hollien asked clinicians who treat chemical dependency, along with a group of everyday people, to listen to recordings made by volunteers when they were sober, then mildly intoxicated, legally impaired, and finally, completely smashed. Listeners consistently overestimated the drunkeness of mildly intoxicated subjects. Conversely, they underestimated the alcohol levels of those who were most inebriated. Professionals were little better at perceiving the truth than the ordinary Joes….

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Did you ever wonder how breathalyzers work? There is a website which will give you a pretty fair idea.

There are many different kinds of “breathalyzers” or breath testing devices. The first of the modern breath testers, manufactured by Smith and Wesson many years ago was called the Breathalyzer.

When I was a young prosecutor we used to call the Smith and Wesson 900A the “Dial-a-Drunk” because the machine’s dial was able to be manipulated by the operator.

Since then, various manufacturers have recognized the growing market and come out with their own models, bearing such names as Intoxilyzer, Intoximeter, DataMaster, AlcoSensor, Alcotest and so on; most of these products have been produced in different model versions, such as the Intoxilyer 4011, 5000 and 8000.

To deal with the confusion, the term “breathalyzer” came to be used as a generic term for any breath testing instrument.

Most of these are evidentiary machines — that is, larger machines generally kept at the police station whose test results are used in evidence. Others are smaller, handheld units carried by officers in the field; generally called PBTs (preliminary breath tests) or PAS (preliminary alcohol screedning). These are less accurate and are usually used as a field sobriety test to help determine whether to arrest a suspect.

The original Breathalyzer operated using a wet chemical method of analysis, employing a disposable glass ampoule of chemicals. Although still occasionally found in law enforcement, this relatively primitive technology was replaced in later machines by infrared spectroscopy, gas chromatography or, mainly in handheld units, fuel cell analysis; a couple of the more recent machines use a combination of infrared and fuel cell.

Here is a great website explaining how these different types of machines work:

http://science.howstuffworks.com/breathalyzer.htm

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