Common Reasons for Breathalyzer False Positives

If you’re stopped by a law enforcement officer who suspects you of drunken driving, you’ll likely be asked to take a breathalyzer test.

When blown into, a breathalyzer can detect someone’s blood alcohol content (BAC). BAC is a measure of how much alcohol is in someone’s system, and when this measurement registers as 0.08 or greater, the individual is considered to be legally drunk.

Drivers who “blow” beyond the legal BAC limit are placed under arrest and taken into custody, where they will be investigated for driving while intoxicated (DWI).

Are Breathalyzers Always Accurate?

Although police officers often rely on breathalyzer results to determine whether or not to arrest someone for DWI, the results that lead to these arrests – and unfortunately, convictions – aren’t always so accurate.

Like a lot of tools and methods at an officer’s disposal, breathalyzers are imperfect and prone to register false positives under several circumstances. Let’s take a look at a few of these below.

Improper Breathalyzer Calibration

Think about how problematic it would be if your car’s gas gauge was calibrated to show a quarter gallon more gas in the tank than you really had – now consider the consequences of an uncalibrated breathalyzer!

A breathalyzer is an instrument used to measure BAC, so it’s important to make sure that it’s properly calibrated to deliver accurate results. When it’s not, two problems can occur depending upon how the device is improperly set up: People who are actually below the legal BAC limit can end up in jail, or those who actually are DWI aren’t getting caught.

In order to prove that a breathalyzer may be faulty or registering inaccurate results, defendants must prove that the device was used more than 150 times or went more than 10 days without a recalibration.

Medical Conditions

Some medical conditions, the medications used to treat them, and even diets can lead to inaccurate breathalyzer results. Conditions such as acid reflux, gastrointestinal reflux disease, and heartburn can all trick the breathalyzer because of the acid present in one’s stomach or esophagus.

Even a ketogenic diet, which is important for managing weight and diabetes, can lead to false positives. This is possible because the body produces acetone, which is a type of alcohol (if you’ve ever heard of stinky “keto breath,” it’s because of this acetone!). A breathalyzer can measure the acetone in someone’s breath and interpret it as BAC, which is especially unfortunate because most people on a keto diet give up drinking alcohol!

Personal Hygiene Products

A lot of personal hygiene products have done away with alcohol in their formulas, but some still have it. There are a variety of everyday products people use to enhance their presence that could set off a breathalyzer.

These can include the following:

  • Mouthwash
  • Perfumes and colognes
  • Breath sprays
  • Toothpaste
  • Hand sanitizer
  • Aftershave
  • Bleach
  • Air freshener
  • Insect repellant

When these products contain alcohol and are used around a person submitting to a breathalyzer test, the breath they take before blowing could collect alcohol molecules floating in the air. These are then blown into the breathalyzer, which could show a much higher BAC than the person actually has.

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