If you show signs of intoxication after being pulled over by the police, the officer may ask you to take a “pretest” or preliminary breath test. The purpose of this portable breath test is to determine if you should be taken to the station for a more sophisticated breath test.
In other words, the PBT is used to establish probable cause to arrest you. Refusal to submit to a preliminary breath test is a Class V misdemeanor carrying a $100 fine and gives the officer probable cause to arrest you to be tested for DUI.