When the government places a location monitor on you or your stuff, it could be violating the Fourth Amendment.

The Supreme Court clarified and affirmed that law on Monday, when it ruled on Torrey Dale Grady v. North Carolinabefore sending the case back to that state’s high court. The Court’s short but unanimous opinion helps make sense of how the Fourth Amendment, which protects against unreasonable search and seizure, interacts with the expanding technological powers of the U.S. government.

“It doesn’t matter what the context is, and it doesn’t matter whether it’s a car or a person. Putting that tracking device on a car or a person is a search,” said Jennifer Lynch, a senior staff attorney at the Electronic Frontier Foundation (EFF)*.

In this case, that context was punishment. Grady was twice convicted as a sex offender. In 2013, North Carolina ordered that, as a recidivist, he had to wear a GPS monitor at all times so that his location could be monitored. He challenged the court, saying that the tracking device qualified as an unreasonable search.

North Carolina’s highest court at first ruled that the tracker was no search at all. It’s that decision that the Supreme Court took aim at today, quoting the state’s rationale and snarking:

The only theory we discern […] is that the State’s system of nonconsensual satellite-based monitoring does not entail a search within the meaning of the Fourth Amendment. That theory is inconsistent with this Court’s precedents.

Then it lists a series of Supreme Court precedents.

And there are a few, as the Court has considered the Fourth Amendment quite a bit recently. In 2012, it ruled that placing a GPS tracker on a suspect’s car, without a warrant, counted as an unreasonable search. The following year, it said that using drug-sniffing dogs around a suspect’s front porch—without a warrant and without their consent—was also unreasonable, as it trespassed onto a person’s property to gain information about them.

Both of those cases involved suspects, but the ruling Monday made clear that it extends to those convicted of crimes, too.

But much remains unclear about how the Fourth Amendment interacts with digital technology. The Court so far has only ruled on cases where location information was collected by a GPS tracker. But countless devices today collect geographic information. Smartphones often contain their own GPS monitors and can triangulate their location from nearby cell towers; electronic toll-collection systems like E-ZPass register, by default, a car’s location and when it passed through a toll road.