Once police have stopped you, the stop must be temporary and last no longer than necessary to effectuate the purpose of the stop (for example, ticket you for the driving violation). From there, the officer need’s independent articulable reasonable suspicion to expand the scope of your stop (for example, asking you to perform field sobriety tests).
As a result, when the police officer approaches you under suspicion of a DWI they are going to ask you questions and observe you and your conduct in an attempt to develop the suspicion necessary to continue investigating. Typically, an officer will ask you if you have had any alcohol, and, if you say yes, they have their reasonable suspicion. You are not required, at any time during the stop, to talk to the officer/s or to answer their questions (with the exception of handing them your driver’s license and proof of insurance). The officer will also look for things like red, watery and bloodshot eyes; slurred speech; slowed movements; difficulty following directions (often they will try to divide your attention by having multiple officers ask you questions); and other similar indicia to develop reasonable suspicion. If, during this interaction, the police believe you are under the influence of alcohol, they will likely request you step out of the car to conduct field sobriety tests and a preliminary breath test.