DUI Alcohol Breathalyzer Tests

Breathalyzers police use to measure a driver’s BAC for later use in court.

By , Attorney · University of San Francisco School of Law

Alcohol breath tests—often called "breathalyzers"—are probably the most common way police determine how much a driver has been drinking. And prosecutors can also use breathalyzer results to prove a DUI charge in court.

Here are some of the basics about breathalyzers and how they're used by law enforcement and prosecutors.

About Breathalyzers

There are two general types of alcohol breath tests: "preliminary alcohol screening" (PAS) tests and evidential breath tests (EBTs).

PAS test machines are small handheld devices that police use in the field to get a general idea of how much a driver has been drinking. However, PAS machines aren't always all that accurate. They can give a ballpark figure of a driving blood alcohol concentration (BAC), but the results are always precise enough to be used as evidence in court.

EBTs, on the other hand, aren't always small enough for police to carry around in their patrol car, but the results are typically much more reliable than their PAS counterparts. EBT devices are often large, stationary machines that police keep at the jail or station. And while PAS machines are normally used prior to an arrest, EBT breathalyzers are generally for post-arrest use.

EBT results—provided the machine was properly serviced prior to use—generally are admissible in court and DMV hearings to prove a driver's BAC. (Still, there are still a number of DUI defenses related to breathalyzer results.)

Can You Refuse a Breath Test?

All states have implied consent laws that require drivers lawfully arrested for driving under the influence to submit to DUI testing. In other words, you don't have a right to refuse if you've been lawfully arrested for a DUI. (However, pre-arrest PAS tests normally aren't mandatory.) Blood and breath tests are the most commonly used, though most states also allow the use of urine tests. Some states allow drivers to select the test, while others let officers decide.

Drivers who refuse post-arrest testing typically face license suspension. The suspension period for a refusal is normally longer than for testing above the legal limit or being convicted of a DUI. A refusal might also lead to having to install an ignition interlock device (IID) and ineligibility for a hardship license. And some states impose criminal penalties such as fines and jail time for refusing a breath test.

Despite the consequences, there may be circumstances where refusing a test is the way to go. Without BAC evidence, it can be more difficult for the prosecution to prove a DUI charge. So, in certain situations, the benefits of refusing may outweigh the drawbacks of taking a test. However, it can be a tough call, and most states (with a few exceptions such as Minnesota) don't allow drivers to consult with an attorney prior to deciding whether to submit to DUI testing.

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