The Supreme Court said Monday that people who borrow rental cars from friends or family are generally entitled to the same protections against police searches as the authorized driver.

The justices ruled unanimously that as a general rule someone who is "in otherwise lawful possession and control of a rental car" has a reasonable expectation of privacy in the car even if the rental agreement doesn't list the person as an authorized driver. That means police can't generally search the car unless they have a warrant or what's called "probable cause" to believe a crime has been committed.

Justice Anthony Kennedy, writing for the court, noted there "may be countless innocuous reasons why an unauthorized driver might get behind the wheel of a rental car and drive it," including that the renter is drowsy or drunk and that the renter and a friend "think it is safer for the friend to drive them to their destination."

The Trump administration had argued that anyone driving a rental car but not listed on a rental agreement does not have an expectation of privacy in the car. That would mean that police who pulled over a rental car with an unauthorized driver could search the car without the person's consent. The Supreme Court rejected the government's argument, saying it "rests on too restrictive a view" of protections in the Fourth Amendment.

Attorneys arguing for protections for unauthorized drivers had noted that 115 million car rentals take place annually in the United States. They said that if the government won, police would have an incentive to pull over a rental car driver who commits a traffic violation because police would know they could search the car if the driver isn't on the rental agreement.

The case the justices ruled in dates to 2014 and involves Terrence Byrd, who was driving a car rented by his fiance when a state trooper pulled him over on a Pennsylvania highway for an alleged minor traffic violation. He acted nervous during the stop and told troopers he had a marijuana cigarette in the car. Officers eventually decided to search the car.

Because the rental agreement didn't authorize Byrd to drive the car, troopers told him they didn't need his consent for the search. And when troopers opened the trunk, they found body armor and about 2,500 little bags of heroin. Byrd later acknowledged he planned to sell the drugs for roughly $7,000, and a court sentenced him to 10 years in prison.