Breathalyzer Tests for DUI/DWI: Frequently Asked Questions

Use these links to jump to different sections:

• What Is a Breathalyzer Test?
• What Is a Fail on the Breathalyzer Test?
• How Does a Breathalyzer Test Work?
• Are Breathalyzer Tests Reliable?
• Will 1 Drink Show Up on a Breathalyzer?
• How Many Drinks Will It Take to Pass or Fail a Breathalyzer?
• Can You Fail a Breathalyzer Without Having Had a Drink?
• Can Breathalyzer Test Results Be Challenged?
• Should I Refuse to Take a Breath Test?
• What Happens if I Refuse a Breathalyzer Test?
• Get an Experienced DUI Defense Lawyer

This article provides answers to frequently asked questions about breathalyzer tests for DUI/DWI cases so that you can have a better understanding and make informed decisions if faced with DUI charges.  

What Is a Breathalyzer Test?

A breathalyzer is a device that estimates a person’s blood alcohol concentration (BAC) based on a breath sample.

Police officers often use breathalyzer tests and Standard Field Sobriety Test procedures (SFST) to determine a driver’s impairment. If a driver fails the SFST or breath test, it gives the police officer probable cause for a DUI arrest.

What Is a Fail on the Breathalyzer Test?

In most states, the BAC legal limit is:

• 0.08 percent for drivers over the age of 21 (in Utah, the limit is 0.05);
• For drivers with a commercial driver’s license (CDL), it’s 0.04; and
• For drivers under the legal drinking age of 21, it’s typically 0.02.

If the breath test results show that your BAC exceeds the legal limit, you fail the breath test.

“If you fail or refuse the standard field sobriety test, some arresting officers will have you blow into a portable breathalyzer machine at the traffic stop,” explains Mark Thiessen, a DUI attorney in Houston, Texas. “The portable breath tester, the one at the roadside, has never been scientifically validated, allowing the results to come into court,” he adds. “Still, officers sometimes use it as a mechanism to estimate where your BAC is.”

If the police officer arrests you on a DUI following a failed field sobriety test, you will undergo additional BAC testing at the police station. In states like Texas, you can choose between a breath test or a blood test. In other states, the choice of which chemical test to use is up to the police officer.

How Does a Breathalyzer Test Work?

A breathalyzer machine measures the amount of alcohol in a person’s lungs based on their breath sample.

When a person consumes alcohol, their body absorbs the alcohol into their bloodstream through the cell membrane lining their stomach. Once in the person’s bloodstream, the alcohol enters different parts of the body, including the lungs, where it diffuses into vapor.

A breathalyzer machine uses a formula to calculate the amount of alcohol in the person’s blood from the amount of alcohol in their lungs. The ratio of breath to blood alcohol levels is 2,100 to 1—so 2,100 milliliters of breath vapor contains approximately the same amount of alcohol as 1 milliliter of blood.

The person simply exhales into the breath test machine to get a BAC reading.

Are Breathalyzer Tests Reliable?

Breathalyzers can offer accurate readings—if they’re a quality device, well-maintained, and administered correctly. But those are all big “ifs,” and results in specific situations can be skewed due to operator errors, machine malfunctions, or bodily and environmental factors.

“Every machine makes mistakes,” explains Thiessen. “And not only could there be machine errors. The human body can also affect the test in various ways,” including:

• The person’s gender and age
• Varying body size and metabolism
• Medications and inhalers
• Medical conditions such as diabetes
• Special diets and food or other substances in the body
• Variations in absorption, elimination, and distribution of alcohol

Will 1 Drink Show Up on a Breathalyzer?

Yes, breathalyzers are capable of detecting small amounts of alcohol. So, if you had one bottle of beer or a glass of wine at dinner, the alcohol from that drink can be detected by a breath test machine.

The fact that a small amount of alcohol can show up on a breath test is not cause for concern in itself. The real issues are whether the amount of alcohol you’ve consumed causes you to drive impaired or if you’ve had enough alcohol to exceed the legal limit for a DUI/DWI charge.

How Many Drinks Will It Take to Pass or Fail a Breathalyzer?

Alcohol affects people differently based on various factors such as gender, weight, and age. And what counts as a single drink is vague in terms of quantity and alcohol content. The impact of 4 ounces of beer with an alcohol content of 4.5 percent differs from an 8-ounce glass of wine with 13.5 percent alcohol content.

As a result, there is no definite number of drinks that guarantees someone will either pass or fail a breath test.

That being said, “there are people who truly have had one beer, and they weigh 170-180 pounds…. [for people like that], there’s almost no way possible that they’re going to be above the legal limit of .08,” says Atlanta DUI defense attorney Ben Sessions.

While a single beer is unlikely to put you in danger of exceeding the legal limit, you must exercise caution, and the more drinks you have, the more cautious you should be. A couple of drinks may be enough to put some individuals over the legal limit.

Can You Fail a Breathalyzer Without Having Had a Drink?

It’s entirely possible to get a false positive on a breath test. Machine and calibration errors can cause false positives, as well as various prescriptions, cough medicines, or mouthwashes with trace amounts of alcohol.

Can Breathalyzer Test Results Be Challenged?

Yes, DUI defense attorneys often challenge breathalyzer test results in court.

Say you failed a breath test and were arrested and charged with driving under the influence (DUI) or driving while intoxicated (DWI).

“Although it might seem like, ‘Oh, I blew over a .08, so I’m guilty’—that’s not necessarily the case,” says Stephen Pfeiffer, a DUI lawyer in Virginia Beach trained in using breathalyzer tests.

“There are nuances you can look at in the administration of a test, such as seeing if it was done correctly or if the officers followed the appropriate protocol,” he says. “If you have an experienced DUI attorney, they may be able to break down… any mistakes in the procedures the officers followed with the breathalyzer, or look into the records of the machine you blew into to see if there are calibration issues or other anomalies.”

Should I Refuse to Take a Breath Test?

The answer to this question is not clear-cut, says Pfeiffer, given DUI laws in Virginia. “It really comes down to a pro-con analysis,” he adds: are you willing to risk driver’s license suspension for refusing a breath test in exchange for a possibly better DUI defense?

Sessions agrees with regards to Georgia DUI law: “I believe you should make [the decision to refuse a breath test] on a case-by-case basis” rather than necessarily defaulting to refusal.

Thiessen, however, with Texas DUI laws in mind, generally urges people not to refuse a breath test for the following reasons:

1. They can use your refusal to blow as evidence of guilt;
2. They can’t test your breath from any drugs or medication, only alcohol;
3. Thanks to shows like CSI, juries tend to trust blood tests more than they do breath tests;
4. Certain counties won’t let you into Pre-Trial programs that result in a dismissal if you refuse;
5. If you blow, we know your result right away and can start fighting your case. Blood doesn’t come back for usually 2-5 months, depending on the county, which prolongs your case.
6. In Texas, they will almost always get a warrant for your blood if you refuse.
7. Even if you have to wait longer to give blood, the analysts can still use retrograde extrapolation calculations to walk the result back in time. So, even if you’re under a 0.08 when you bleed, they can still try to calculate it back hours before. 

“If you refuse a breath test in Texas, almost 24/7 now, police officers are getting warrants for a blood sample,” he says. “The officer will immediately go fill out an affidavit for a blood warrant and go to a judge—and they don’t even have to physically go to the judge; they’re faxing or scanning it to the judge in the middle of the night. The judge signs the warrant and sends it back, and then they take you to get your blood drawn.”

He adds that “refusing a breath test used to be good advice back in the 2000s, but now it’s outdated.”

Ultimately, there isn’t a definitive answer that would apply to all states and circumstances. It depends on specific factors such as:

• The risk you’re willing to take;
• How intoxicated you think you are when asked to take a breath test;
• Whether there are alternative tests that will be used regardless;
• Whether the fact that you refused to take a test be admissible in court.

What Happens if I Refuse a Breathalyzer Test?

Every state has an implied consent law. By driving in the state, you have consented to BAC testing if asked by a police officer who has reasonable suspicion that you’re intoxicated.

You can still refuse to take a breath test, but that refusal will carry penalties—namely, the temporary loss of driving privileges.

“Note that driver’s license suspension is a separate civil case,” says Thiessen. “In Texas, it’s called an ‘ALR’ or Administrative License Revocation hearing. Say, on a first DUI/DWI offense, you refuse to take the breath test. The state will try to come after you for a six-month suspension. You have 15 days from the date of the DUI arrest to request an ALR hearing to see if the state will successfully suspend your license.”

Get an Experienced DUI Defense Lawyer

If you’re facing criminal charges for a DUI/DWI, even on a first offense, contact a criminal defense attorney with experience defending drunk driving cases for legal advice.

An experienced DUI defense attorney will understand your state’s DUI/DWI laws and legal defenses. They will also be familiar with the alcohol testing procedures that law enforcement officers use and the science behind them.

Use the Super Lawyers directory to find a DUI/DWI defense attorney in your area. For more information on these legal issues, see our DUI/DWI law overview.