In every U.S. state, it is illegal to operate a motor vehicle with a blood alcohol content that is 0.08 percent or above. With this BAC or higher, police will consider drivers to be intoxicated and the drivers could be arrested and charged with DUI. There are three ways to test an individual’s BAC: through blood, urine and breath.
Since blood and urine testing are difficult to administer in the field after an officer pulls over a driver, testing the breath with a handheld Breathalyzer machine has become the standard way to determine drivers’ BAC during a routine traffic stop. Police will also administer field sobriety tests to determine if an individual is too drunk to drive.
Still, Breathalyzer test results are not always viewed as reliable by courts. Indeed, they are not always reliable because different factors could throw off the results of a breath test to render false positives with regard to an individual’s level of inebriation. False positives could be caused by something the person ate, the timing of the test following a drink of alcohol (if, for example, there is still some alcohol remnants in the person’s mouth), and a wide variety of other factors.
Because Breathalyzer test results are often dismissed by courts due to the possibility of inaccuracy, law enforcement officers will usually rely on the results of a field sobriety test administered in the field, blood tests performed in a controlled medical setting after arrest and other kinds of tests to prove that a driver was in fact DUI.
To answer the question of whether Breathalyzer tests work, however, it is important to look at a bigger picture. Although breath tests may not work to convict a driver of DUI, they could work to clue an officer in on performing additional tests, such as a field sobriety test and blood work. In this sense, the Breathalyzer machine serves an important purpose for police.
Source: BACtrack, “Are Breathalyzers Accurate?,” accessed Dec. 07, 2015