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How Does a Breathalyzer Work



If you are ever caught driving drunk and you have your first DUI, also known as a DWI, experience, you may be unfamiliar with the breathalyzer test. A breathalyzer is a device that can estimate your blood-alcohol level.

If your blood-alcohol level is higher than the legal limit, you will be arrested for drunk driving.

There are certain rules that vary from state to state about whether a police officer may force you to take a breathalyzer test. It is important that you know these rules, as well as how a breathalyzer works in the event that you get pulled over.

Blood Alcohol Content

In 2005, the legal blood-alcohol limit in all states was set to below .08. This number means that your blood is eight one-hundredths percent alcohol. Therefore, if you are caught driving with a blood-alcohol level of .08 or above, you are breaking the law, and an officer will place you under arrest.

In addition, if you are under the age of 21, your state may have a zero tolerance law. Zero-tolerance laws are used to discourage underage drinking and driving. Under these laws, the legal blood-alcohol level is drastically reduced, sometimes to as low as .01. The punishments can be instantaneous and severe. Specifically, under zero-tolerance laws your license can be automatically suspended for 90 days to six months.

The Breathalyzer Test

When a police officer pulls you over, he or she does not know immediately that you are intoxicated. This is why the police office may employ one of several on-site tests to develop what is known as probable cause. Probable cause means the officer has a valid reason to believe you committed a crime.

One way to establish probable cause is to administer a breathalyzer test. A breathalyzer test uses a small, portable device known as a breathalyzer. This device has been approved for use by the National Highway Traffic Safety Administration.

For the breathalyzer test, the officer will ask you to breath into the device. The device detects traces of ethanol in your breath. It then provides an estimate of your blood-alcohol content based on these ethanol levels. If the device shows your blood-alcohol level to be at or above .08, the police officer will have established probable cause and will have the authority to place you under arrest.

Refusing the Breathalyzer Test

The consequences of refusing a breathalyzer test can be severe depending on your state's laws.

If you do refuse to take a breathalyzer test, you may have your license automatically suspended from 90 days all the way up to a year. Not only that, but you will be prosecuted for drunk driving and be subject to the usual types of DUI punishment, which may include fines, jail time, and community service.

Breathalyzer Errors

Breathalyzers are not perfect pieces of equipment and are prone to errors. This may be able to help you during the trial phase of your DUI case because your attorney may be able to call into question the accuracy of the breathalyzer as a type of target="_blank">legal defense.

The following are examples of breathalyzer errors:

  • Calibration: Most breathalyzers require recalibration at least once a year to maintain accuracy. If the breathalyzer has not been recalibrated in some time, it might give a false reading.
  • Interfering substances: There are non-alcoholic substances that can contribute to a false reading. Specifically, people who are diabetic can have high levels of a certain chemical called acetone that the breathalyzer may read as alcohol.
  • Mouth alcohol: The breathalyzer can only detect traces of alcohol in your breath, not alcohol in your system. Although the assumption is that the alcohol it is detecting represents the alcohol in your blood, you may have higher traces of alcohol in your mouth, which can contribute to a false reading.