“If a police officer pulls you over and believes you might be driving under the influence, obviously, they’ll ask those question of giving you their drivers license, proof of registration, and insurance. Then they might ask where you’re coming from tonight, might ask how many drinks you’ve had, things like that.
If they believe you might be drinking, looking at your eyes, whether your speech is slurred, any objective symptoms that they see, they might ask you the Nystagmus test where they have you follow their pin or their finger to see if you could be under the influence.
If they feel that you are, at that point, they may ask you to step out of the vehicle and then begin to ask you some pre‑investigatory questions where they don’t need to Mirandize you. The answers to those questions might further their opinion that you might be under the influence. Then they might proceed to conduct what they call “field sobriety tests.”” – Philip Greenberg