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Why you should (politely) refuse a preliminary breath test (PBT).

In most states, it is common for the police to request that you submit to a preliminary breath test during the course of a drunk driving “investigation”. In Michigan, most people are best advised to refuse the test.

What is a preliminary breath test (PBT)?

A PBT is a small handheld device that attempts to measure blood alcohol content by measuring the alcohol contained in your breath as you exhale into the PBT. To do this, most PBTs make use of a fuel cell that oxidizes the alcohol in your breath as it passes over the fuel cell. This oxidation process alters the electrical current flowing through the device and it attempts to calculate your blood alcohol content based on this change in electrical current. Generally speaking, the results of a PBT are not admissible to prove the amount of alcohol in one’s body in a trial for driving under the influence.

Among many other problems, PBTs can produce falsely high results when other substances are exhaled into the PBT, adverse weather conditions exist, or the police officer isn’t properly trained in its use.

What is not a PBT?

Generally speaking, a PBT is a device that is small, portable, and most often administered on the road-side. This is in contrast to an evidential breath test — which in Michigan is a Datamaster test. The Datamaster will most often look like this:

Datamaster Evidential Breath Tester

Datamaster Evidential Breath Tester

However, the company the produces the Datamaster has finally come out with a newer model that looks like this:

New Datamaster

New Datamaster

Should I take a PBT on request of a peace officer?

Probably not. In Michigan, most people would be well advised to refuse a police officer’s request to perform a PBT.

MCL 257.625a(2)(d) provides that ” a person who refuses to submit to a preliminary chemical breath analysis upon a lawful request by a peace officer is responsible for a civil infraction.” Due to additional penalties for commercial driver license (CDL) holders, refusing a PBT may not be appropriate for a CDL holder.

The final analysis:

For the ordinary driver, refusing a PBT will result in a civil infraction (a non-criminal ticket — like a speeding ticket) and a fine.  Submitting to the PBT may give the officer the probable cause that he needs to arrest you.

Joshua Blanchard is an attorney licensed in the state of Michigan. He provides an aggressive criminal defense to those who need it most. For more information, or to confidentially discuss your situation, please call him at 877-MICH-DUI or e-mail josh@joshuablanchard.com.


This information may not be appropriate for your particular situation, including but not limited to drivers licensed in other states, drivers under the age of 21, drivers with a commercial driver license, drivers carrying a concealed weapon pursuant to a valid conceal pistol license, drivers on probation or parole, drivers who have been involved in a serious accident, or others. To understand how the law impacts your unique situation, you should always consult with a qualified attorney before taking any action.