What Does a Breathalyzer Measure?

What Does a Breathalyzer Measure
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Chances are, you already know what a breathalyzer is. You’ve probably seen one on TV or in a movie. The scene is always the same—a cop notices a suspicious person on the road. The person seems drunk, so they pull them over and put the person through a breathalyzer test. Is he too drunk to drive, or is he completely sober? For some, bigger questions swim in their head. What does a breathalyzer measure anyway?

Blood alcohol content or BAC

To understand how breathalyzers work, and to finally answer the looming question, “What does a breathalyzer measure?” you must first understand blood alcohol content or BAC. This is actually the answer to everything.

BAC is the term for the amount or percentage of alcohol in your system. When you consume alcohol, it is absorbed into your bloodstream. When your blood reaches your lungs, the alcohol molecules pass through the air sacs and out of the body when we breathe.

What does a breathalyzer measure?

The breathalyzer test determines the molecules of alcohol found in one’s breath and configures a percentage. It is this percentage that stands as your BAC, and also as the determinant of your state of intoxication.

What is the right BAC?

Reaching, and going beyond a BAC level of 0.08% means that you are considered “legally intoxicated” in the United States. This means that having a BAC of 0.08% and higher can land you a DUI or a DWI charge.

What factors affect BAC?

Every person reacts to alcohol differently. You may notice that some of your friends turn red after just one bottle of beer, while others can binge drink a whole bottle of wine and still be up and about. This is because there are many factors that affect each person’s BAC. Some of these factors include:

  • The amount of alcohol a person is drinking
  • The alcohol levels present in the drink
  • How fast the person is drinking
  • The person’s age
  • The person’s weight
  • The person’s metabolism
  • How much food and water the person has consumed prior to drinking alcohol

How long does it take for your BAC to go back to normal?

The answer depends on your current BAC level and the magic number: 0.015%. What is this number? It is the pace at which the body’s BAC levels drop for every hour that you don’t consume any alcohol. So, to measure how long it will take for your BAC to go back to normal, you must determine what your current BAC level is, and deduct 0.015 for every hour that you don’t ingest alcohol. Count the hours, and there you have it!

Why is it important to know these facts?

Drunk driving is a leading cause of death in the United States. In 2015 alone, over 10,000 people died in alcohol-impaired car crashes. That amounts to about 30% of all road-related deaths in the country. Because of these alarming rates, the police make it their mission to keep anyone from putting their lives at risk.

Many cops are strict and will stop anyone who is driving suspiciously. They will put these drivers under breathalyzer tests to determine whether their subjects are too impaired to drive or not.


What does a breathalyzer measure? A breathalyzer measures the amount of alcohol (or blood alcohol content) found in a person’s system. It does this by analyzing the alcohol molecules present in a person’s breath. The breathalyzer comes up with a number that represents a percentage. This percentage must be below 0.08% in order for someone to be cleared to drive.


Drinking and driving is a huge risk. Not only do you risk landing in jail, but you also put your life and the lives of others in danger. If you find yourself enjoying a night out with your friends, you can choose to pace yourself, entrust a non-drinker with the keys to your car, or simply wait it out until your body is in a better state.

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