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 Missouri, the law regarding DUI/DWI (driving under the influence/driving while intoxicated) can apply to a person who is in 'physical control' of a vehicle, even if they are not actively driving. This means that if an individual is found by police sitting, lying, or sleeping in their vehicle while under the influence of alcohol, they could potentially be arrested for DUI/DWI. Factors that law enforcement may consider include whether the individual is in the driver's seat, whether the vehicle's engine is running, the individual's level of consciousness, and the location of the vehicle's keys. If the police encounter someone in such a situation, they may conduct a welfare check and inquire about recent vehicle operation and alcohol consumption. Depending on the responses and observations, the police may then request the individual to submit to sobriety tests or a breath or blood test. If the evidence suggests the individual was in physical control of the vehicle while intoxicated, they may be arrested for DUI/DWI. It's important to note that even if someone has pulled over with the intention of 'sleeping it off,' they can still face legal consequences if deemed to be in control of the vehicle while impaired.