What is the accuracy of a breathalyzer test?

Written by robert alley
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What is the accuracy of a breathalyzer test?
A Breathalyzer is used to test for alcohol content in a person driving a car. (yellow car, a honda Japanese sport car model image by alma_sacra from Fotolia.com)

A Breathalyzer is a machine used to measure blood-alcohol levels in people suspected of driving an automobile under the influence of alcohol. Due to the strong penalties for a conviction and the importance attached to the results of the Breathalyzer test, the accuracy of the device's readings is an ongoing source of controversy.

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Although often used generically, Breathalyzer is the brand name for a machine to measure blood-alcohol content. It was developed and manufactured by Smith and Wesson in the 1950s. Today there are other machines that perform the same function, such as Intoxilyzer, Intoximeter and Alcosensor, manufactured by different companies. These devices are essential tools in the enforcement of laws against driving after consuming alcohol. They must be accurate or they cannot serve their purpose.

What is the accuracy of a breathalyzer test?
Throughout the years, Breathalyzers have become crucial to enforcement of alcohol and driving laws. (Vintage Automobile image by Ray Carpenter from Fotolia.com)


The legal system has come to rely upon the Breathalyzer in the enforcement of alcohol-related crimes involving automobiles. Law enforcement officers are still important, but the Breathalyzer and its accuracy are built into the law. If the Breathalyzer reading is 0.08 or more, the presumption is that the operator is impaired by alcohol. The federal government in 1998 created financial incentives for states to adopt the .08 standard. Until then, each state had its own standard and some were higher than 0.08.

What is the accuracy of a breathalyzer test?
The magic number: 0.08. (eight ball image by Georgios Kollidas from Fotolia.com)


The Breathalyzer is a machine, and its accuracy depends upon two factors: proper function and human operation. The second factor is pretty straightforward. A Breathalyzer is only as accurate as the operator. After a person blows air into the Breathalyser's mouthpiece, a chemical reaction takes place which measures the blood-alcohol content. The operator must ensure that the person properly blows into the Breathalyzer. The final step involves the operator turning the knob on the Breathalyzer to obtain the correct reading. This is crucial and human error can occur, especially in a case that is borderline 0.08. The first factor is more complex. The Breathalyzer must be properly maintained and tested periodically to ensure its accuracy. Like any machine, it must function properly in order to fulfil its intended use.


A Breathalyzer is not as accurate as a blood test. According to Alcohol Test Info, the Breathalyzer can vary as much as 15 per cent from the actual blood-alcohol concentration. There are many reasons for the variation, the main being that the Breathalyzer is measuring alcohol levels from breath as opposed to blood. The alcohol is in the blood, so testing the blood will be more accurate.

What is the accuracy of a breathalyzer test?
A blood test is more accurate than a Breathalyzer. (blood testing image by John Keith from Fotolia.com)


The accuracy of a Breathalyzer relates to how the machine functions. The law is now that a 0.08 reading on a Breathalyzer is a presumption of driving under the influence. Therefore all that matters to sustain that presumption is that the Breathalyzer machine is properly functioning and that the operator made no mistakes during the testing. That does not mean that guilt is determined by the Breathalyzer. The presumption can be rebutted by evidence that the driver was not driving under the influence of alcohol. So while the Breathalyzer is important, it is not the final word.

What is the accuracy of a breathalyzer test?
The accuracy of a Breathalyzer is determined in a court of law. (Justice image by MVit from Fotolia.com)

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