Tyack Law News + Blog

What Can Cause a False Positive Breathalyzer Test?

November 04, 2019

How Does a Breathalyzer Work?

A breathalyzer is a device used by law enforcement to check the alcohol content in a person’s system. Most often these are used during sobriety tests to ensure that drivers on the road are not under the influence of alcohol. This technology is inserted into the mouth of a person and reads the air they exhale. A reading on a breathalyzer test determines if the person’s BAC is within the legal limit or not.

What Does a Positive Reading Mean?

If you’re given a breathalyzer test and it reads that you are over the legal limit, it is likely that there is a high level of alcohol in your body. Today, technology in these devices produces an accurate reading. However, there are some instances where you may find yourself with a false positive breathalyzer.

What Can Cause a False Positive Breathalyzer?

Several factors can cause a false positive breathalyzer test. These include:

  • Calibration of the equipment
  • Medical conditions
  • Time the test is given in relation to drinking
  • Contamination

Equipment Calibration

Like other technology, breathalyzers must be calibrated frequently to ensure they are working properly. If a test is administered without proper calibration, it can cause a false positive breathalyzer. For law enforcement to know they are getting the most accurate reading, the device must be set at specific settings and kept that way.

Medical Conditions

Medical conditions and medications that create acid in the stomach and esophagus could result in a false positive breathalyzer. That’s because they increase the BAC levels in the blood and may leave some presence of alcohol in the mouth.

Time of Test

If a breathalyzer is administered at a certain point when the alcohol is being absorbed, it can cause a false positive. This is because the blood alcohol content may rise and then fall after being consumed and it may appear that a person is over the legal limit even though their actual blood alcohol content may be below.


Breathalyzer tests could easily be contaminated by outside factors, like the device not being cleaned properly or chemicals in the air. Any of these factors can cause the reading to be a false positive breathalyzer result.

What Besides Alcohol Can Set Off a Breathalyzer?

Breathalyzers were designs to detect the blood alcohol content of a person, and technology has advanced to make these devices more accurate than ever. However, some factors in the body that aren’t alcohol can result in a positive reading. Some things that can make you fail a breathalyzer besides alcohol include:

  • Medications
  • Acetone


As we stated before, medications that create an excess of acid in the body can result in a false positive breathalyzer result.


Acetone is in the breath of every person, and sometimes these levels may be high enough to cause a false positive reading on a breathalyzer. Hypoglycemia not only causes the presence of acetone, it can also produce symptoms to that of intoxication. Low-carb diets also increase acetone levels and can result in false positives.

What Happens if You Fail a Breathalyzer?

If you fail a breathalyzer test, law enforcement is going to assume there is a high level of alcohol in your body. You will likely be arrested and charged with a DUI. If you feel that your breathalyzer test was a false positive, you may have to seek the help of an attorney to support your claim in court.

Can You Deny a Breathalyzer?

You can deny a breathalyzer test but it is not wise to do so. If law enforcement has reasonable suspicion that you were under the influence while driving (speeding, swerving, running a stop sign) you have no case against yourself and a judge will assume you have “consciousness of guilt.”

Conclusion: What Can Cause a False Positive Breathalyzer Test?

While some factors can result in a false positive breathalyzer test, like medications, certain diets, or problems with the equipment, most positive readings indicate a person is under the influence. If you’ve been charged with a DUI because of a positive breathalyzer, contact a DUI attorney to help you with your case.


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