A person who believes they have had too much to drink to safely or legally drive may sit, lie, or fall asleep in their vehicle in a parking lot or parking space outside of a bar or restaurant, or may pull off the road and park to “sleep it off.” When the police observe a person occupying or sleeping in a parked car they may investigate if the car is illegally parked (on the side of the road or elsewhere) or for the stated purpose of checking on the well-being of the occupant of the vehicle.

After knocking on the window and attempting to wake the occupant of the vehicle the police will typically ask if the occupant was recently operating the vehicle and whether the occupant has had anything to drink. Based in part on the occupant’s answers to these questions the police may request the occupant submit to a breath or blood test, perform field sobriety tests, and may ultimately arrest the occupant for DUI/DWI.

Laws defining DUI/DWI criminal offenses vary from state to state and often include a person who is in physical control of a vehicle as being within the definition of operating a vehicle. Based on such a broad statutory definition of operating a vehicle—and depending on other factors such as (1) whether the occupant was in the driver’s seat of the vehicle or the back seat or passenger seat; (2) whether the vehicle’s engine was running; (3) whether the occupant was awake or asleep; and (4) whether the key, if any, was in the ignition—the police may arrest the occupant for DUI/DWI.

In Arizona, a person found in a parked vehicle who is suspected of being under the influence may be subject to a DUI investigation. Arizona law considers a person to be in actual physical control of a vehicle if they have the current ability to operate the vehicle, regardless of whether they are driving at the time. Factors such as the location of the person in the vehicle, whether the engine is running, the person's state (awake or asleep), and the position of the keys are taken into account to determine control. If the police find someone in a parked car, they may investigate to ensure the vehicle is not illegally parked and to check on the occupant's well-being. During this interaction, if the police suspect the occupant has been drinking, they may ask questions, conduct field sobriety tests, and potentially request a breath or blood test. Depending on the occupant's responses and the officer's observations, the person may be arrested for DUI if they are found to be in actual physical control of the vehicle while under the influence.