In 1897, barely 10 years after the invention of the automobile, a 25-year old London taxi driver named George Smith became the first person ever arrested for drunk driving after slamming his cab into a building. He later pled guilty and was fined 25 shillings.
In the United States, it would take another 10 years before laws against drunk driving would go into effect. New York led the way in 1910. At that time, states did not generally require licenses to operate automobiles. The laws generally imposed fines for drunk driving, but did not, obviously, suspend licenses since licenses were not required in the first place.
For much of the early part of the 1900s, drunk driving was proved by a police officer or other witness’ testimony that the driver appeared intoxicated, swerved, slurred words, had glassy eyes, and so forth, while driving. North Carolina – and all states – still recognize this method of proving impairment as a legitimate way to convict someone of drunk driving.
But scientists started searching for an objective way of measuring alcohol impairment. An early method was a balloon-like device called a “Drunkometer” and developed by a professor of biochemistry in 1936.
The search for a more accurate device that was easier for police to use led to the invention in the mid-1950s of the breathalyzer. An Indiana State Police Captain invented that used photometry (measuring the perceived brightness of light passing through the breath of test subject) to produce a Blood Alcohol Concentration (BAC) that was much more accurate than that produced by the “Drunkometer,” but still not completely accurate.
Today’s breathalyzer machines, mostly a product of 1980s science and engineering, rely on infrared spectroscopy. Light is passed through a chamber into which a subject has breathed. Sensors measure the difference between a full light spectrum and the light produced after it passes through the breath. Since the chemical processes resulting from the consumption of alcohol generate fumes in the breath that block light, the sensors can gauge (supposedly) the BAC of the subject. (It’s important to note that the breathalyzer only produces a proxy result. It doesn’t actually measure the BAC of the subject, which can only be done by actually testing the blood of the person.)
Another major change was the implementation of BAC restrictions on drivers. In the 1950s, many states set the legal limit at .20 or .15. Over time, especially in the 1970s and 1980s, the limits were lowered. By the late 1990s, every state in the country had accepted .08 as the legal limit because of the requirements of federal highway funding laws.