When law enforcement pulls you over, it is overwhelming. Your heart may be racing and your head filled with a myriad of thoughts as the officer approaches your vehicle. If the officer suspects you have been drinking and driving, he or she could ask you to take a roadside breath test. Officers use these devices to determine whether motorists are driving with a blood alcohol content level that is over the legal limit of 0.08%. Yet, some breath tests tend to yield inaccurate results, which could lead to a wrongful DUI arrest.

Breath test devices measure blood alcohol content indirectly. A blood sample is the most accurate way to determine blood alcohol levels, but they are impossible to conduct alongside the road. Instead, you must exhale into a tube connected to a breath test. The machine then measures the amount of ethanol alcohol in the sample and converts it to a BAC reading. When compared to an actual blood test, however, a breath test can differ by at least 0.15%. That means that one in every four people who use a breath test device will have a higher reading than if they were to take a blood test.

There are certain factors that can affect breath test readings, according to the State University of New York at Potsdam. The machines pick up more than just ethanol. These include the following:

  • The relative humidity and temperature of the air
  • Pollution, dirt and smoke in the air
  • Residual blood, food, vomit or drink in the mouth
  • Cellphone and police radio electrical interference
  • Fumes from gasoline, cleaners and cigarette smoke

If an officer has not calibrated a breath test properly or is not using the machine correctly, it can lead to skewed results as well. It is best to be aware of these factors and keep them in mind if you should have to take a roadside breath test.