The Preliminary Breath Test is the portable, handheld breath tester police officers use after the field sobriety tests to add a little more weight to their probable cause for arresting you.
The PBT gives a breath alcohol score. The score is not admissible in court and the PBT is generally considered unreliable. However, it has been allowed in court to show the presence of alcohol – just not the amount.
That said, if your PBT score is more than .08 – you are going to jail. The officer will find that he perceived you to be under the influence. The only time the PBT works in your favor is if you are stone cold sober or damn close.
Refusing the PBT is not refusing the breath test. There are no penalties in Missouri for refusing the PBT. However, there may be penalties on the street for refusing to comply with the officer’s requests. You could wind up under arrest when you might not have been arrested if you took the test.
There is no hard and fast rule for whether or not to participate in field sobriety tests, the PBT, or even the breath test at the station. Just remember, police are required to give you 20 minutes to contact a lawyer before the test — IF YOU ASK FOR IT.