Breathalyzer Basics: How They Work, Whether You Can Refuse One

At DUI traffic stops, it's common practice for a police officer to test a driver's breath alcohol content with a breathalyzer machine.

Many people are familiar with the concept of a breathalyzer, even if they have never used one: a driver blows into the machine and it analyzes the content of the breath do determine how much alcohol the person has in their system.

Still, a lot of myths about breathalyzers exist. Here's a look at how these machines work and what happens if a driver refuses to take a breath test.

How Do Breathalyzers Work?

First of all, let's establish some basics: blood alcohol content (BAC) is a measurement of the percentage of alcohol in someone's bloodstream.

In the U.S., DUI laws are heavily influenced by BAC measurements: in all 50 states, a driver with a BAC of .08 percent or greater can be charged with DUI, whether or not she appeared impaired at the time.

Breathalyzers are a tool used to estimate BAC, which they do by:

  • Capturing a person's breath: This occurs when the person breathes into the machine.
  • Measuring breath alcohol content: The breathalyzer is equipped with technology that measures the volume of alcohol in a person's breath.
  • Converting to BAC: The breathalyzer then uses a formula that converts the breath alcohol measurement to a blood alcohol measurement.

Can Breathalyzers Be Wrong?

Because breathalyzers measure breath alcohol and DUI laws are written in terms of blood alcohol, it is possible for a breathalyzer to incorrectly analyze a person's breath sample.

A measurement might be incorrect under the following circumstances:

  • Improper calibration: A breathalyzer that has not recently been "tuned" may give a false reading.
  • Certain physiological conditions: The National Highway Traffic Safety Administration has found that certain people (including those on diets and those with diabetes) may have acetone present in their breath, which may cause improper breathalyzer readings.
  • Formula variables: The conversion formula from breath alcohol to blood alcohol assumes a standard ratio (2100 to 1) of alcohol in blood to alcohol in breath. In reality, though, people's ratios vary considerably. Thus the estimated BAC from a breathalyzer could differ substantially from the actual BAC a blood test would provide.
  • Mouth alcohol: Non-absorbed alcohol (as from mouthwash) can cause falsely high readings from a breathalyzer; however, mouth alcohol content tends to drop quickly, so subsequent breathalyzer readings should resolve this issue.

Can I Refuse a Breathalyzer?

A better question is, perhaps, whether you can afford to refuse a breathalyzer.

Most states permit drivers to refuse a breathalyzer test; however, almost all have steep refusal penalties. For example:

  • Jail time: In some states, a first-time refusal of a breathalyzer test can lead to jail time. Breathalyzer refusal by those with a DUI conviction on their records can also lead to jail time in some states.
  • Fines: Many states fine drivers who refuse a breathalyzer test, and the fines aren't small. In some states, a first refusal can cost a driver $10,000.
  • Increased insurance rates: New Jersey levies a $3,000 insurance surcharge ($1,000 per year for three years) on drivers who refuse a breathalyzer once; those who refuse multiple tests get steeper fines.
  • Alcohol treatment programs: Certain states require that those who refuse breathalyzers complete alcohol counseling or treatment. The driver, of course, must foot the bill for such services.

It's important to note, too, that a driver can be convicted of DUI even without taking a breathalyzer. That's because DUI laws work like this:

  • De facto DUI: Anyone with a blood alcohol level of .08 percent or greater may be convicted of DUI simply because that BAC currently meets the legal definition of "impaired."
  • Impairment DUI: A person who refuses to take a breathalyzer or whose BAC is below the legal limit may still be convicted of a DUI if the police can prove that he or she was impaired by alcohol. That is, if the police can show evidence that the driver's ability to operate a vehicle was affected, that person may be convicted of DUI.

DUI laws are complicated and DUI convictions often come with serious legal consequences. If you have been charged with DUI, you may want to speak with an attorney in your area.

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