A breathalyzer test is a diagnostic device that measures how much alcohol is in the air a person breathes out. It can be used to estimate blood alcohol content (BAC), or how much alcohol is in the blood.

In most states, the legal level for driving is 0.08%, but some states have lower levels.

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.

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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 breathalyzer, 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.

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).

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.

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.