The first roadside breath alcohol testing instrument developed for the exclusive use of police was invented in 1938 by W.J. Harger. Cumbersome and unreliable, the "drunkometer" was replaced in 1954 when Dr. Robert Borkenstein, a former captain of the Indiana state police force, introduced the breathalyzer. Like the drunkometer, Borkenstein’s invention was designed for roadside use by police to determine a driver’s alcohol impairment levels.

A breathalyzer works by measuring the concentration of alcohol in an individual’s breath. Since the measure of alcohol in a person’s breath is related to alcohol levels in a person’s blood at a ratio of 2,100 ml to 1 ml, a breathalyzer is able to factor an individual’s level of intoxication, known as blood alcohol concentration (BAC). If BAC is .08 or higher, police consider an individual too impaired to legally operate a motor vehicle. This can result in loss of a driver’s license, prosecution and possible jail time.

While Harger and Borkenstein created their inventions with the intent of assisting police, breath alcohol analyzers are now widely used by other law enforcement officials, professionals in alternative fields and private citizens.

Probation officers monitor BAC levels of parolees through random tests to ensure compliance with court orders. Similarly, corrections officers often employ breathalyzers to safeguard against intoxication among inmates. Medical professionals use breath alcohol analyzers to determine a patient’s BAC so a safe course of treatment can be chosen in consideration of a patient’s alcohol consumption.

Educators, suspicious of a student’s sobriety, may use a digital breathalyzer, depending on the laws governing their school’s state and municipality. In most instances, a minor is considered intoxicated if their BAC is .02, significantly lower than the .08 allowed for individuals who surpassed the legal drinking age of 21.

Whether purchased or received as gifts, private citizens use breath alcohol analyzers to avoid endangering themselves or others on roadways.

Regardless of whether a breathalyzer is used by a trained professional or individual, BAC results can be impacted positively or negatively by some common factors. Many mouthwashes and breath fresheners list alcohol among their ingredients and, if they are used immediately before a breath test is administered, may inflate BAC measures, for example. Dieters and diabetics may be prone to inaccurately high BAC results because acetone, a compound found at higher levels in the blood of these populations, is sometimes misidentified as alcohol by the testing devices, thus producing higher test results.

On the other hand, rigorous exercise may cause a breathalyzer to produce a falsely low reading of a person’s BAC if a test is conducted shortly after activity ceases.