Alcohol breath tests, commonly called breathalyzers, measure blood alcohol content (BAC). The more intoxicated a person is, the higher their BAC.

This test is often used by law enforcement to determine whether you’ve been drinking and driving. The results of breathalyzers administered by police can be used in court.

It’s a crime to drive with a BAC level of .08 percent or higher, the federal standard. Some states have different laws that further impact penalties, and it depends what kind of vehicle is being operated.

Alcohol breath tests are also sold for personal use. But depending on the brand, many at-home versions of breathalyzers are less sensitive and can have a higher margin of error.

We’ll overview how alcohol impairs driving, what taking a BAC test is like, and how you can stay safe both on and off the road.

Sobering statistics

Every year, thousands of people in the United States die from collisions involving drunk drivers. Driving under the influence (DUI) remains a serious risk to public safety.

  • In 2020, 11,654 people died in traffic accidents involving alcohol impairment.
  • Nearly a third of driving fatalities involve alcohol impairment.
  • According to a 2020 study, men account for the vast majority of DUI offenses, although rates for women have risen in recent years.
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In an alcohol breath test like the breathalyzer, there’s a mouthpiece and two chambers filled with liquid that are connected to a meter that looks for any changes in color.

You exhale into the mouthpiece. Your breath enters a chamber filled with potassium dichromate and other chemicals, which are a red-orange color. Alcohol reacts to this solution and changes the liquid’s color to green. The degreeof color change is related to the level of alcohol in your exhaled breath.

A photocell (a special sensor that changes with light exposure) then compares the difference in colors. This color difference results in an electrical current, which is then converted to a numerical value for the BAC.

An alcohol breath test will give you a numerical value of your BAC. This is the weight of alcohol in a certain volume of your blood.

Alcohol is directly absorbed through your stomach and small intestine and then goes into your bloodstream until your liver metabolizes (processes) it.

According to the National Highway Traffic Safety Administration, here’s how different levels of BAC are measured and how it translates to your driving fitness:

BAC levelEffects
.02some loss of judgment, relaxation, mood changes, impaired visual functioning and attention
.05lowered inhibitions, exaggerated behavior, trouble steering the wheel, lowered emergency response, impaired ability to track moving objects
.08impaired muscle coordination, judgment, focus, self-control, and ability to accurate comprehend your speed
.10noticeable deterioration of reaction time and control, slurred speech, unable to stay in your lane position or brake correctly
.15vomiting may occur (unless there’s a tolerance buildup), losing sense of balance, can’t safely keep vehicle control or pay attention to the activity of driving

The accuracy of alcohol breath tests can vary depending on the type of test used.

A 2014 study found that several personal-use breathalyzers weren’t always “sufficiently sensitive to test safety to drive after drinking alcohol.” This can be life threatening if you get behind the wheel based on the wrong results, thinking you’re less impaired than you are.

User error can also affect a home BAC test’s results, creating incorrect readings.

While these researchers found most alcohol breath tests sold to the public had an accuracy of 90 percent or above, one was as low as 26 percent. And even a 10 percent error rate can contribute to impaired drivers on the road.

But another 2017 UK study overviewing 208 people’s BAC results from at-home alcohol breath tests found these devices could also overreport BAC. The authors emphasized more studies into test accuracy are needed, but they ultimately recommended at-home tests as a valuable tool in appraising BAC levels to prevent drunk driving. They cited the average accuracy of both these tests and police ones at around 95 percent.

A key finding is that at-home tests were less accurate at finding the impacts of very recent drinking. The above study found that for the most accurate results, at least 15 minutes should pass between your last drink and taking the test.

The choice to consume alcohol is a personal one, but if you do drink alcohol, it’s your responsibility to be safe about it. This means drinking responsibly and taking steps to ensure the safety of yourself and those around you.

Things you can do to drink responsibly include:

  • Drinking in moderation. This is considered two drinks or less a day for men, and one for women.
  • Plan a designated driver. If you’re expecting to drink before getting in a vehicle, plan to have a designated driver who remains alcohol and substance free to ensure safe transportation. Among people who regularly drink together, consider rotating this responsibility.
  • Find another way home. This could look like:
    • calling a family member or friend for a ride
    • using a rideshare service or taxi
    • taking public transportation
    • staying longer or overnight at your current location if possible, allowing yourself to sober up

There are also steps you can take to limit alcohol’s intoxicating effects on your system, but remember this doesn’t guarantee you’re fit to drive:

  • eat something before and during your alcohol consumption to help your body absorb the substance
  • alternate alcoholic drinks with glasses of water
  • drink slowly and pace your consumption
  • be aware of the specific alcohol content of the drinks you consume

Alcohol breath tests, or “breathalyzers,” are tests that can measure your BAC and help you determine if you’re too intoxicated to drive safely.

Alcohol and other substances can significantly impair your reaction time, judgment, and focus. DUI causes thousands of deaths each year.

While breathalyzers are often used by law enforcement, single-use tests and others are also sold to the general public. But while these tests can be an essential tool for keeping drunk drivers off the road, they may not always be sensitive enough to accurately capture blood alcohol levels.

When consuming alcohol, always drink responsibly. Set a designated driver or have a backup plan for getting home safe if you drink to the point of impairment. Even if your home BAC test registers as low, if you’ve had several drinks and feel impaired despite testing under the limit, don’t drive. Nothing is worth risking your life or the lives of others.