If you have been pulled over on suspicion of drunk driving in Montana, you know firsthand the process law enforcement officers use to determine whether you are intoxicated. Officers often use a roadside breath test device to measure your blood alcohol content level. 

However, these devices do not always provide accurate and reliable results. In fact, according to the State University of New York at Potsdam, at least one in four people who use a breath test device will have inflated results. This could lead to a wrongful DUI arrest and possible conviction. 

How do breath test devices work?

Breath test devices measure the amount of ethanol alcohol in an exhaled breath sample. It then converts this amount to a blood alcohol content level. Yet, it does not measure the amount of alcohol in the blood itself. 

While different models of breath test devices use differing methods of obtaining BAC level results, some are more accurate than others. The least reliable are handheld device, which are easiest for law enforcement officers to use during traffic stops. 

What causes inflated results?

When comparing BAC levels obtained from a breath test device to actual blood tests, the results may vary by as much as 15%. Other substances contain structures similar to ethanol, such as methyl groups. The device may also detect these groups and may erroneously measure them as alcohol. 

Substances and environmental factors that can alter breath test readings include the following: 

  • Residual food, drink, blood or vomit in the mouth 
  • Cigarette smoke, dirt or pollution in the air 
  • Relative humidity and temperature of the air 
  • Electrical interference from cellphones and officer radios 

Machine readings may also vary depending on whether you have just run, are hyperventilating or have inhaled gasoline, paint or paint thinner fumes.