Most DUI cases start with a police officer observing a suspect driving a vehicle in an erratic manner or at least in such a way that one or more traffic laws are violated. This allows the police officer to stop the driver and have an encounter. However, occasionally, we see DUI cases that begin when the suspect is not driving at all. Many of these DUI cases begin when a police officer observes a person sleeping in a vehicle that is parked, sometimes legally, sometimes illegally, and sometimes in the roadway. Other times, a concerned citizen sees a person sleeping in his/her car and calls the police to check it out.
It is certainly not illegal to sleep in your car, so the police are not permitted to detain you or arrest you based on that alone. Of course, where your car is parked when you are sleeping in it will be a factor in whether the police officer has sufficient cause to move forward with a criminal investigation. If your car is in your driveway or in a regular parking spot, the police officer will have less of a legal reason to wake you up and question you. If you are partially in the roadway, there would be more evidence to suggest driving while impaired from alcohol or some other problem which gives the police officer more legal reason to investigate.
Generally, when a police officer sees a driver asleep in a vehicle, that police officer can come to the vehicle to check on the driver. Sleeping alone is not sufficient evidence of impairment from alcohol so the officer cannot detain the driver and start a DUI investigation. The police officer can check and see if there appears to be a medical emergency and if so, go into the vehicle to help. However, the officer cannot assume a medical problem; the officer must have specific evidence of a medical problem. The officer cannot assume the driver is drunk either. If there are alcohol containers near the driver, that may be enough evidence of a DUI to move forward with an investigation, but absent specific evidence of alcohol or drugs, the police officer cannot start a DUI investigation. Basically, sleeping in the car can prompt a police officer to look inside the vehicle, but unless there is specific evidence of a medical problem or alcohol/drugs, the officer has to leave the driver alone after a brief encounter.