When it comes to enforcing laws against driving under the influence, breath tests are one of the most powerful tools available to authorities, and one that they rely on heavily.
However, the tests are not infallible. There are multiple factors that can affect their accuracy.
Factors involving the tests
Sometimes there is a problem with the test itself that causes it to give an inaccurate reading. Law enforcement primarily relies on electronic breath tests. These are usually very accurate. However, according to WebMD, they could give an inaccurate reading if they require a software update, need their batteries replaced or require recalibration.
There are also manual breath tests available. They are less accurate than electronic devices. Therefore, law enforcement rarely uses them. Nevertheless, if law enforcement does administer a manual breath test, the driver has reason to be suspicious of the result.
Factors involving the driver
Sometimes ordinary actions that are not illegal on the part of the driver could confuse the testing device and result in a false positive on the breath test. For example, many people use oral hygiene products that contain small amounts of alcohol, such as breath fresheners and mouthwash. There is evidence of these products producing false positives on breath tests, as well as cigarette smoke.
Trace amounts of alcohol remaining in the mouth could produce a false positive on a breath test if the driver had a drink less than 15 minutes before taking it. One drink alone would not be enough to elevate blood alcohol concentration above the legal limit of 0.08%, yet the lingering presence of alcohol could give the machine the impression of a BAC elevated to a dangerous level.
Drivers should be aware of the factors that can produce false positives on a breath test. If the court uses the results against a driver, he or she may have legitimate questions to raise about the accuracy.