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What Is the Difference Between a Preliminary Breath Test and an Evidentiary Breath Test?

Posted on in Drunk Driving / DUI

TX DWI lawyerDrunk driving suspects are often asked to blow into a breath-testing device during traffic stops. The device measures the alcohol in the person’s breath which can be used to assess their intoxication level. According to Texas law, a driver with a blood alcohol concentration (BAC) of 0.08 percent or more is considered to be intoxicated and subject to prosecution for driving while intoxicated (DWI). Therefore, the results of breath tests heavily influence most DWI cases.

Many people are unaware that there are two different types of breath tests used by police officers in most states, including Texas. It is important to know how these breath tests can affect a DWI case and what to do if you were charged with drunk driving based on a breath test result.

Portable Breath Tests Are Preliminary Tests

When police suspect a person of driving under the influence of alcohol, they may require the person to complete field sobriety tests or a breath alcohol test—commonly referred to as a “breathalyzer.” Police must have “probable cause” to arrest someone, which means that the officer must be able to cite an objective reason why they believe the person committed a crime. The small, easily transported breathalyzers that most people are familiar with are preliminary breath tests. These tests have only one purpose: establishing probable cause.

Portable breathalyzers that are carried around by police are not accurate enough to be used as direct evidence in a DWI case. You have the right to refuse to take a preliminary breath test. However, refusing the test does not mean that you will avoid getting arrested. Police can use slurred speech, the smell of alcohol on your breath, field sobriety test results, or other circumstances as probable cause for a DWI arrest.

Testing at the Police Station Is What Really Counts

Once a person is arrested on suspicion of DWI and taken to the police station, they will almost certainly be asked to take another breath alcohol test—one that is much more accurate than the roadside version. This test is conducted on a large, stationary device and is referred to as an evidentiary breath test or mandatory breath test. If you refuse to take an evidentiary breath test upon your arrest for DWI, your driver’s license will automatically be suspended for 180 days. As the name implies, the results of an evidentiary breath test are admissible as evidence in a DWI case.

Keep in mind that being arrested and charged with drunk driving is not the same as being convicted. You still have a chance to present a defense on your behalf. Although evidentiary breath tests are usually more reliable than preliminary breath tests, they are not perfect. Issues with the timing or administration of the test, device defects, and inadequate calibration are just some of the problems that can lead to inaccurate or invalid results.

Contact a Denton County DWI Defense Lawyer

If you or a loved one were arrested on suspicion of drunk driving, contact Marsala Law Group. Our Denton DWI defense lawyers can investigate your case and help you defend yourself. Call 940-382-1976 for a free consultation to learn more.


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