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How do breath test devices work?

On Behalf of | Mar 23, 2022 | Traffic Offenses And DUI

When law enforcement officers pull motorists over on suspicion of drinking and driving, they often use a myriad of tests to determine whether the driver is indeed intoxicated. One of the methods used is breath test devices.

While these handheld monitors are easy to use along the roadside, the results they give are often unreliable and inaccurate. In fact, erroneous results may lead to wrongful arrests and possible DWI convictions.

Measuring blood alcohol content levels

When you blow into a breath test device, the machine measures the amount of ethanol alcohol found in your system. It then converts that number to a blood alcohol content level. If the results read 0.08 or higher, you run the risk of getting arrested and charged with a DWI.

Researchers have found, however,  that breath test device readings are not comparable to blood alcohol concentrations obtained from an actual blood test. In fact, research from the State University of New York at Potsdam shows that one in four people who take a roadside breath test will show elevated BAC results.

Evaluating the readings

In addition to measuring ethanol alcohol in a breath sample, breath test machines may pick up other methyl groups that are similar in structure. Other environmental factors can also affect breath test results. These include the following:

  • Dirt and pollution in the air
  • Relative humidity and temperature of the air
  • Residual food, drink, blood or vomit in the mouth
  • Fumes from gasoline, paint, cleaners or paint thinner
  • Cigarette smoke
  • Electrical interference from officer radios or cellphones

It is important to realize that a breath test reading is not always an accurate indicator of whether a motorist is actually intoxicated.