A breath test measures tiny particles of alcohol from air deep in the lungs as you breathe out, reflecting you blood alcohol level.
A breath test is one of three kinds of chemical test you could be given if suspected of DUI. The others are blood tests and urine tests. Each one is used slightly differently, but all three have the same goal: to measure the amount of an intoxicating substance in your body.
How Breath Tests are Used
Not all DUI’s involve alcohol, but a breath test can only detect alcohol in your breath. It cannot detect illegal drugs. A different kind of test is used if you are suspected of driving under the influence of drugs.
There are two main kinds of breath test machine: small portable devices that officers carry with them, and desktop devices that are used at a police station. The portable devices are often used for a roadside breath test, known as a PAS. In most cases you can decline to take a PAS if the officer asks (but there are exceptions). If you are arrested for DUI, however, you will likely be asked to take a breath test using the device back at the station. Once you have been arrested it is illegal to refuse the test.
Breath tests are often called Breathalyzers. This isn’t always correct. Breathalyzer is a specific type of breath test device. You can read more about Breathalyzers here.
How Does a Breath Test Work?
The way a breath test works is relatively crude. It is supposed to measure the amount of alcohol from air deep in your lungs. This alcohol comes from the blood passing through the lungs, so it measures how much alcohol is in your blood stream, or your blood alcohol concentration (BAC). But it can be thrown off by many factors:
- Burping, vomiting or drinking right before the test
- Certain diets or medical conditions
- The presence of mouth alcohol from other sources like mouth wash
Defending Against Breath Test Results
The results of a breath test can be disputed on several grounds. It could be mistaken because the device did not work correctly, because the officers didn’t do the test correctly, or because you have a condition that interferes with the test results. The most common challenges to a breath test are:
- The machine was not maintained or calibrated correctly, meaning its data cannot be trusted
- The machine has a history of skewing high, when looking at data from hundreds of cases
- Officers did not perform a proper 15 minute “observation period” to make sure you didn’t burp
- You had acid reflux or eat a high protein, low carb diet—either of which interferes with the test.
To defend against a breath test, you don’t have to prove you were stone sober. You just have to show the machine may have been off. If your BAC may have been lower than what was recorded by the test, it could win your case.
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