Colorado DUI Defense: Breathalyzer Test Accuracy

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By: Bill Henry
PublishedJul 1, 2019
4 minute read

breathalyzer test

Summertime is synonymous with backyard barbecues, festivals, and refreshing libations. It’s also a time for expanded use of sobriety checkpoints and the breathalyzer.

In July 2018, Colorado law enforcement officers arrest 340 people for DUI during the Independence Day weekend.

Robinson & Henry, P.C. encourages you to always drive sober. But you should know the following important legal information if you are suspected of or charged with a DUI .

Robinson & Henry, P.C. offers consultationsSchedule a meeting with one of our DUI criminal defense attorneys at (303) 688-0944 if you’ve been charged with DUI and you feel your breathalyzer test produced false results.

Breathalyzer Test Interference

Law enforcement officials use the breathalyzer to determine if someone is intoxicated. These tests are not perfect. Improper administration can skew the results.

Before we delve into everything that can go wrong with the breathalyzer, let’s go over how it works. We’ll also quickly explain the difference between breathalyzer tests at a check point and the breath test that follows an arrest.

Field Sobriety Check Points

Police look for a number of DUI indicators at sobriety checkpoints and traffic stops. Police may ask you to perform several field sobriety tests:

  • the walk and turn
  • stand on one leg
  • an eye test – involuntary jerking called “nystagmus”

Finally, officers may ask you to take a preliminary breathalyzer test.

IMPORTANT: You do not have to take any field sobriety tests, including the preliminary breathalyzer test. They are not mandatory in Colorado. You may decline to take them without any legal consequences.

“No person shall be…compelled in any criminal case to be a witness against himself…”
                                                                    – The Fifth Amendment

REMEMBER: You have the right to remain silent, even at a sobriety check point. You do not have to answer questions about whether you’ve been drinking or where you’ve been. Be polite. Let the officer know you choose to remain silent.

You’ll likely still be arrested for suspected DUI or DWAI if the officer has probable cause that you are intoxicated. They will ask you to take an evidentiary breathalyzer test at the police station. You face serious consequences if you decline to take an evidentiary breathalyzer.

How the Evidentiary Breathalyzer Test Works

In Colorado, law enforcement agencies use the Intoxilyzer® 9000, or I-9000, for evidentiary breath tests.

The Intoxilyzer® 9000 measures the amount of ethanol in your breath. According to the device’s manufacturer, the I-9000 uses infrared wavelengths to sample the breath.

Here’s a simplified explanation of how the Intoxilyzer® 9000 works:

A beam of infrared light passes through the tester. You breath into the machine. Alcohol in your breath affects the infrared light. The more alcohol on your breath, the more the amount of light passing through the machine decreases.

The breathalyzer compares the initial infrared light to the infrared light passing through during your breath sample. A computer provides an approximate breath alcohol content.

The Breathalyzer Test Problem

There are other chemicals that can absorb infrared light besides ethanol. Acetone can give false positive results.

The maker of the Intoxilyzer® 9000 claims it is more accurate than previous models. The I-9000 should detect certain interferents, like acetone, and relay an invalid test message.

However, some studies find breathalyzer tests can produce falsely-inflated results when exposed to other chemicals.

False-positive results mean the difference between a DUI (.08) and a DWAI (.05) charge or a wrongful charge altogether.

So let’s explore some of the issues that can create inaccurate breathalyzer test results.

Factors That Can Affect Breath Alcohol Test Results

Accurate breathalyzer results are crucial in DWAI and DUI arrests. But outside factors can compromise your DUI test results.

Improper Calibrating

This one’s a biggie. The Intoxilyzer® 9000 must be adjusted before it is used in order to produce the most accurate reading. As a result, the machine can give false results if it is not properly calibrated.

Electronic Interference

Radio frequency transmissions can interfere with the Intoxilyzer® 9000. Police radios and cell phone calls can affect DUI test results.

The I-9000 is equipped with a radio frequency interference (RFI) detection system. The breathalyzer should alert the operator it detected RFI.

However, Counterpoint, The Journal of Science and the Law reported active cell phone calls had to be within inches of the breath test for the machine to detect radio interference. The Counterpoint study also produced false-negative and false-positive readings without the breathalyzer machine indicating there was any radio frequency interference.

Due to RFI, many police departments around the country ban cell phone use during evidentiary breathalyzer tests.

Residual/Mouth Alcohol

Residual mouth alcohol is alcohol left behind in the mouth after you consume an alcoholic beverage or use other items that contain alcohol.

You don’t have to drink alcohol to have residual mouth alcohol. Common foods, medicines, oral hygiene products, and other substances can alter DUI test results.

  • Mouthwash
  • Cough syrup
  • Breath spray
  • Chewing gum
  • Menthol smokeless tobacco
  • Some asthma inhalers
  • White breads

Some breads can result in a false positive test. Many breads require yeast, and when yeast ferments it produces small amounts of alcohol. Eating a slice of white bread or other breads can affect a breathalyzer test or a car’s ignition interlock system.

Generally, mouth alcohol dissipates in 15 minutes or less. The Intoxilyzer® 9000 detects residual alcohol. The machine should indicate invalid samples.

Mouth Alcohol & Medical Ailments

A number of health conditions and diseases can artificially inflate testing outcomes. For instance, diabetics can have exponentially higher acetone levels than those who do not have the disease.

Also, someone who has gastroesophageal reflux disease, or GERD, can have inflated tests. GERD can cause undigested alcohol to regurgitate into the mouth.

Mouth Alcohol & High-Protein Diets

Diets that involve eating lots of protein and consuming no carbohydrates can cause your body to use fat for fuel. As a result, your body creates acetone as a byproduct. Some of that acetone escapes your body through your mouth in the form of isopropyl alcohol.

The I-9000 detects ethanol, but isopropyl alcohol can interfere with the test. If that’s the case, the machine should give the operator a warning signal.


It’s possible to have artificially inflated DUI test results if you work with or around certain harsh chemicals, such as acetone.

Administration Error

Law enforcement officials are trained to give proper breath alcohol tests. Inaccurate results can occur if administration procedures are not followed.

For instance, officers should ensure the DUI suspect has not consumed alcohol for 15 to 20 minutes before administering the test. Therefore, if police do not wait long enough your results can be skewed.

I Think My Breathalyzer Test is Wrong. Can I Fight It?

Of course you can, and you should. You should not accept a wrongful DUI charge or conviction.

Robinson & Henry’s DUI criminal defense attorneys can investigate the circumstances that may have resulted in your test having an inflated reading.

Our DUI lawyers will review your test results. They will also look for mistakes made by police.

Mistakes can include:

  • no probable cause for the stop
  • breathalyzer protocol errors
  • Miranda rights not read

If you have a DUI or DWAI charge call us at (303) 688-0944 . We may be able to help.

Schedule your initial assessment by phone or online. Our DUI criminal defense attorneys will work to build a strong defense for you.

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