After a traffic stop and any field sobriety tests, the first stage of the criminal process in a DUI case begins when a police officer places the suspect under arrest. An "arrest" occurs when a person has been taken into police custody and is no longer free to leave or move about. The use of physical restraint or handcuffs is not necessary. An arrest can be complete when a police officer simply tells a crime suspect that he or she is "under arrest", and the suspect submits without the officer's use of any physical force. The key to an arrest is the exercise of police authority over a person, and that person's voluntary or involuntary submission.

A police officer may usually arrest a person in the following circumstances:

The Police Officer Personally Observed a Crime

If a police officer personally sees a person commit a crime, the officer may lawfully arrest that person. For example:

A police officer pulls over a vehicle that is being driven erratically, and after administering a Breathalyzer test, sees that the driver's alcohol intoxication level is more than twice the state's legal limit for safe operation of a vehicle. The police officer can legally arrest the driver for DUI.

The Police Officer Has "Probable Cause" To Arrest

When a police officer has a reasonable belief, based on facts and circumstances, that a person has committed (or is about to commit) a crime, the officer may arrest that person. This belief, known as "Probable Cause", may legally justify a DUI arrest in certain situations where strong indications of DUI are present, but administration of a chemical test is refused or is otherwise not possible. For example:

A police officer pulls over a vehicle that is being driven erratically. The officer notices empty beer bottles in the back seat and the strong odor of alcohol on the driver's breath. Though the driver refuses to submit to a Breathalyzer test, the officer may lawfully arrest him or her based on a probable cause belief that a DUI has been committed.