The Supreme Court came to a landmark decision Monday morning, voting unanimously that police agencies must obtain search warrants before they can install GPS tracking devices on the vehicles of suspects.

Although all justices voted that police must obtain a warrant, the reasoning differed among those involved. In a 5-4 split over the explanation, the majority of the justices said that the Fourth Amendment’s protection of “persons, houses, papers, and effects, against unreasonable searches and seizures” was implied with a person’s private property, such as their automobile.

Had the justices voted otherwise, local law enforcement agencies would have been legally protected to affix small devices on the cars of suspects, without their knowing, in order to monitor their every move on public roads.

In 2005, Washington D.C. police thought they had that right when they bugged the vehicle of a suspected cocaine dealer and used the info to follow him for more than a month and eventually land a conviction on the charge of drug distribution. The conviction was later overturned, however, when the legality of the process was called into question. Lacking a valid warrant, a federal appeals court overruled the decision and had the lengthy sentence previously put on defendant Antoine Jones removed.

The Obama administration argued against the appeal and insisted that the matter make it to the Supreme Court. Now nearly seven years after Jones was bugged without a warrant, the highest court in America has decided that a warrant would be required in all cases in the future.

Although all justices voted that police must obtain a warrant, the reasoning differed among those involved. In a 5-4 split over the explanation, the majority of the justices said that the Fourth Amendment’s protection of “persons, houses, papers, and effects, against unreasonable searches and seizures” was implied with a person’s private property, such as their automobile. Justices Antonin Scalia, John Roberts, Anthony Kennedy, Clarence Thomas and Sonia Sotomayor voted in the majority.

Justices Samuel Alito, Ruth Bader Ginsburg, Stephen Breyer and Elena Kagan added that, while in agreement, the practice would also violate a person’s “reasonable expectation of privacy.”

In the case of Jones, authorities in favor of GPS tracking had insisted that installing a small, physically non-invasive device while an automobile is parked in public property did not necessitate a warrant, citing that the installation would be conducted in public space and would only track a vehicle on public roads.

Justice Scalia remarked his opposition for some time, saying last year that “When that device is installed against the will of the owner of the car, that is unquestionably a trespass … an unreasonable search and seizure.”

“If you win this case then there is nothing to prevent the police or the government from monitoring 24 hours a day the public movement of every citizen of the United States. … So if you win, you suddenly produce what sounds like ‘1984’,”Justice Breyer added.

Before Monday’s decision was made, similar cases awaited smaller courts across the country. Earlier this month, U.S. Magistrate Judge David Noce ruled in favor of the Federal Bureau of Investigation, who were arguing that they didn’t need a warrant to affix a device to a suspect in St. Louis, Missouri. “When police have reasonable suspicion that a particular vehicle is transporting drugs, a warrant is not required when, while the vehicle is parked in a public place, they install a non-invasive GPS tracking device on it for a reasonable period of time,” Noce said in his decision.

The ACLU called the ruling a “critical decision for defending the Fourth Amendment, which protects Americans from unreasonable searches. It is the first time in 20 years the Supreme Court had to consider the constitutionality of location-tracking technology, the organization said.