You're sitting at a red light. A glance in your rear-view mirror shows a law enforcement officer behind you. When you look again, she's focused on your tag while typing something into her computer. Is that officer running your tag? Is she allowed to do that? And just what does "running your tag" mean?
Courts have decided that you have no privacy rights in the tag on your vehicle. That means that the police aren't violating the 4th Amendment when they enter your tag information into a database to learn about both the vehicle and the driver. Recently, Florida began using Automated License Plate Readers (ALPR). An ALPR instantaneously scans license plates in the area – storing a digital image of the plate, the time, date, location, and camera information. The ALPR compares license plate information to a database of crimes and criminals. Even with no action on the part of a human being, information about your license plate may be recorded anytime and anywhere because courts don't feel you have a right to privacy in that information.
An important case is currently in front of the United States Supreme Court. In Kansas v Glover, SCOTUS must decide whether a car can be pulled over because the registered owner has a suspended license. An officer in Kansas ran Mr. Glover's plate and discovered that the vehicle's registered driver (Mr. Glover) had a suspended license. The officer pulled the vehicle over without confirming if Mr. Glover was driving or seeing any traffic infraction. Mr. Glover was driving and was charged with driving on a suspended license. This case has implications for the privacy rights of drivers across the entire country.
Your rights under the 4th Amendment can be confusing. There are different rights in your car versus your home. And different rights for passengers versus drivers.