Breathalyzer test: How it works, what it measures, and accuracy (2023)

A breathalyzer test uses a diagnostic device to estimate a person’s blood alcohol content (BAC). By blowing into the device, a person can determine whether they are over the legal limit to drive.

Consuming alcohol can be an enjoyable activity for some people. However, many people may not realize how quickly alcohol can affect them and how much it can impair their ability to perform routine tasks. Drinking and driving is a dangerous combination. Evidence notes that in the United States, it is responsible for roughly 28 deaths a day, which costs the U.S. approximately $44 billion each year.

The use of breathalyzers can help reduce the number of motor vehicle accidents that involve an alcohol-impaired driver. This device calculates the concentration of alcohol in the breath to determine whether a person has consumed too much alcohol to drive safely.

In this article, we discuss how the breathalyzer test works and provide tips on how to drink safely.

A note about sex and gender

Sex and gender exist on spectrums. This article will use the terms, “male,” “female,” or both to refer to sex assigned at birth. Click here to learn more.


(Video) How Do Breathalyzers Work?

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The term BAC refers to the concentration of alcohol in a person’s system. Measuring the amount of alcohol, or ethanol, in a person’s system requires a blood, saliva, urine, or breath sample.

An alcohol breath test refers to BAC measurement through breath. This test will typically require a person to blow into a device known as a breath analyzer, or


, which is usually portable.

An individual can use a personal device to measure their own BAC. However, it is more common for law enforcement to request a breathalyzer test if they suspect that a person has been drinking alcohol and not complying with a drinking-related law, such as driving under the influence of alcohol.

How it works and what it measures

(Video) How do Breathalyzers work? | Chemistry behind the breathalyzer | Alcohol testing Devices|In English.

A breathalyzer test measures BAC, which reflects the percentage of alcohol in a person’s blood. Authorities can use BAC levels to gauge a person’s level of intoxication. Following alcohol consumption, the body absorbs this chemical through the stomach lining into the bloodstream. As blood passes through the lungs, some alcohol evaporates and moves into the lungs.

The concentration of alcohol in the lungs relates to the concentration present in the blood. By using a partition ratio, it is possible to determine the BAC almost instantly from the air a person exhales rather than requiring a blood sample. The ratio of breath alcohol to blood alcohol is roughly 2,100:1. This means that roughly 2,100 milliliters (ml) of breath will contain the same amount of alcohol as 1 ml of blood.

Using the partition ratio, a breathalyzer can calculate a person’s BAC. Generally, a breathalyzer is able to measure BAC due to a chemical reaction. The alcohol vapor in a person’s breath reacts with an orange solution known as potassium dichromate. When alcohol is present, this solution turns green. This color change creates an electrical current, which the breathalyzer can convert into a value to determine the BAC.

Generally, the BAC limit in the U.S. is 0.08%. However, in Utah, the limit is 0.05%. For an adult, a BAC of 0.08% may correspond to consuming four or more drinks — typically five or more drinks for a male — in 2 hours. If a person’s BAC measures 0.08, it means that there are 0.08 grams of alcohol per 100 ml of blood or that their blood is 0.08% alcohol.

The following chart summarizes different BAC levels and their potential effect on a person’s perceptions and capabilities.

BAC levelEffect on perceptions and capabilities
0.01–0.05relaxed, a slight “buzz,” less inhibited, and alert
0.06–0.10emotional, numb, sleepy, reduced memory and coordination
0.11–0.20mood shifts, mania, inappropriate behavior
0.21–0.30aggression, depression, impaired vision and reasoning
0.31–0.40unconsciousness or coma
0.41 and overpotentially fatal

Generally, there are two different types of breath analyzer tests: preliminary alcohol screening (PAS) tests and evidential breath tests (EBTs).

(Video) Is the Breath Test Accurate in Determining Blood Alcohol Content?

PAS tests refer to the small handheld devices that police may use in the field to determine a person’s BAC. However, these machines are not always accurate. EBTs describe larger, stationary machines that are more reliable, which the police keep at the jail or station. A law enforcer may use a PAS machine prior to an arrest and then an EBT after the arrest to confirm the results.

Breathalyzers may also use different techniques to measure BAC. These can include:

  • electrochemical fuel cell breathalyzers
  • infrared optical sensor breathalyzers
  • semiconductor breathalyzers

Ongoing research is also developing breathalyzers that are compatible with smartphones and looking at other ways to measure intoxication using smart devices.

Many different factors can affect the accuracy of a breathalyzer test. For example, other compounds in the breath, the temperature, a person’s health, and human error may affect the accuracy of readings. Additionally, the volume of air that a person exhales when performing the test can affect the accuracy of the results.

Some evidence suggests that personal breathalyzers could be a good indicator of BAC. Research comparing the results of personal breathalyzer tests with those of police-grade breath analyzers found that the devices classified individuals into similar drunk driving categories at a rate of 94.1%.

However, although PAS tests and personal devices can be a useful indicator of a person’s BAC, they are not always accurate. This is why a court may require either an EBT result or a blood test to confirm a person’s BAC. Therefore, it may be advisable to use a personal device only as guidance and avoid driving after consuming an alcoholic beverage.

How much alcohol a person drinks within a period of time essentially determines the BAC level. However, other factors can also influence a person’s BAC, such as:

  • Body composition: Individuals with a smaller stature will likely experience intoxication quicker. However, as body fat does not absorb alcohol, people with higher body fat levels will have a higher BAC due to a higher proportional concentration of alcohol in their lean tissues.
  • Gender: Females typically have less alcohol dehydrogenase, which is the enzyme responsible for metabolizing alcohol.
  • Use of other drugs: Taking other drugs, such as over-the-counter, prescription, or illegal drugs, can affect how the body processes alcohol and result in adverse events.
  • Stomach contents: Having food in the stomach can help slow the processing and absorption of alcohol.
  • Type of drink: Drinks with a higher alcohol content will result in a higher BAC. For example, 1.5 ounces (oz) of a spirit is usually equal to 12 oz of beer. Additionally, the body absorbs carbonated beverages, such as spirits mixed with soft drinks or champagne, more quickly.
(Video) Are Breathalyzer Tests Always Accurate?

If a person wishes to consume alcohol, it is advisable to do so in moderation. According to the Dietary Guidelines for Americans 2020–2025, this means drinking no more than one standard drink per day for females and two per day for males.

Some tips for drinking alcohol safely and responsibly include:

  • keeping a count of how much a person is drinking
  • spacing drinks out and consuming water in between alcoholic beverages
  • avoiding drinking alcohol on an empty stomach
  • drinking alcohol in safe spaces
  • avoiding taking medications or other drugs while consuming alcohol

Additionally, it is highly advisable to avoid driving any vehicle after consuming alcohol. People should arrange a designated driver or have an alternative plan to get home, such as a cab ride.

A breathalyzer typically refers to a handheld device that analyzes a person’s breath to determine their blood alcohol concentration. This device can be a useful way to measure intoxication and let people know when they are past the legal limit to drive. Legal limits may vary, but generally, it is illegal for a person with a BAC of 0.08% or above to drive. People should drink responsibly and make alternative arrangements, such as a cab ride, to get home.

(Video) Breathalyzer blowback: Device's accuracy questioned


What is the accuracy of a breathalyzer test? ›

In fact, reliable scientific studies show that breathalyzers have a 50% margin of error when compared to blood tests. A whole host of factors affect a breathalyzer BAC reading, including age, gender, rate of consumption, medication, and emotional state. A breathalyzer cannot account for all of these factors.

What does a breathalyzer test measure? ›

A breath alcohol test determines how much alcohol is in your blood. The test measures the amount of alcohol in the air you breathe out (exhale).

How is alcohol measured on a breathalyzer? ›

An infrared cell directs infrared energy through the sample and any unabsorbed energy at the other side is detected. The higher the concentration of ethanol, the more infrared absorption occurs (in much the same way that a sunglass lens absorbs visible light, alcohol absorbs infrared light).

Are breathalyzers 100% accurate? ›

Although breathalyzers are commonly used to indicate intoxication in drunk driving cases, they aren't 100% accurate. If you've been charged with a DUI/DWI, understanding when breathalyzers can provide false readings may be crucial to your defense.

What factors affect breathalyzer accuracy? ›

Nonetheless, a variety of outside factors can directly affect the accuracy of breath test results, as can errors in the administration of Breathalyzer devices.
Breathalyzer Results and Other Chemical Compounds
  • Burping and belching.
  • Denture.
  • Periodental disease.
  • Vomiting.

How does a breathalyzer accurately measure alcohol concentration in blood? ›

Photocells in the breathalyzer measure the degree of color change in the sample containing alcohol and produce an electric current that allows the operator to determine the BAC of the person providing the breath sample.

How does a breathalyzer work chemistry? ›

In the Breathalyzer™, alcohol reacts with the reddish-orange potassium dichromate solution and turns green. The degree of the color change is directly related to the level of alcohol in the expelled air.

What is meaning of breathalyzer? ›

Britannica Dictionary definition of BREATHALYZER. — used for a device that police use to test someone's breath in order to measure how much alcohol is in that person's blood.

What can affect a breathalyzer test? ›

Medications That Can Affect Breathalyzers
  • Asthma medications. Albuterol, salmeterol, and budesonide are asthma medications that may affect breath tests. ...
  • Nyquil and OTC medications with alcohol. ...
  • Anbesol in Oral Gels. ...
  • Mouthwash and Breath Spray. ...
  • Fumes. ...
  • Gastroesophageal Acid Reflux. ...
  • Ketones.
Jul 15, 2020

How often are breathalyzers wrong? ›

Generally, breathalyzer tests are only accurate approximately 40% of the time. Factor into that statistic that the testing equipment itself has an inherent margin of error between . 005 and . 02% in its BAC readings.

Which is more accurate breathalyzer or blood test? ›

Blood tests generally produce more accurate results than breathalyzers and other breath tests. Blood tests directly measure the suspect's actual BAC. Breath tests only indirectly measure someone's BAC. Blood tests are also less susceptible to environmental factors that can skew the results.

What is the margin of error on a breathalyzer test? ›

Considering the fact that BAC readings have been considered irrefutable evidence of driving while intoxicated, some may be surprised to find out they never should be. Uncontested and peer reviewed studies show a 50 percent margin of error when comparing Breathalyzer result readings to actual BAC results.

Is breathalyzer higher than BAC? ›

It is uncommon for a breathalyzer to read higher than a blood test. From the above biological process, it is evident that the cell membranes in the stomach absorb most of the alcohol in the blood before it circulates to the respiratory system. Raw blood provides more accurate results compared to a breath sample.


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