The Supreme Court has long held that police don't need a warrant to search a motor vehicle if they have probable cause to think it contains evidence of a crime. But does the so-called "automobile exception" apply to a vehicle parked in a location that would ordinarily require a warrant to access?

In a strikingly broad ruling in 2015, the Supreme Court of Virginia said it did. Going beyond the nationwide rule that cars can be searched without a warrant—a doctrine based on the fact that their mobility makes it easier to move or destroy important evidence before a warrant is issued—the Virginia justices held in Collins v. Virginia that the automobile exception trumps even the Constitution's requirement that police must have a warrant to search a home.

The case was then appealed to the U.S. Supreme Court, which heard oral arguments yesterday. The outcome could have wide implications for Americans' Fourth Amendment rights.

The story began when a police officer, without a warrant or consent, walked up a private driveway and lifted a tarp off a motorcycle parked in a partially enclosed car-port connected to the back of a house. The officer was looking for a distinctive motorcycle whose rider had previously eluded him at high speed, but a check of the VIN number revealed that the bike was stolen. Having found this evidence, the officer arrested Ryan Collins, whose girlfriend lived in the home.

Collins wants to suppress the evidence, arguing that it was the fruit of an illegal search. If such searches are permitted, Collins' lawyers and a number of pro-privacy groups argue, the suspected presence of a vehicle could be used as a pretext for warrantless searches of nearly any location.

In yesterday's oral arguments, several justices seemed skeptical of Virginia's reasoning. As Chief Justice Roberts noted, the state's doctrine could theoretically authorize a warrantless search of Jay Leno's house based on the presence of cars inside. When Justice Sonia Sotomayor asked Acting Virginia Solicitor General Trevor Cox if he thought "the police can break into anything, go anywhere where they see the car, whether they [are] at that place legitimately or not," Cox answered "yes"; that prompted Justice Neil Gorsuch to interject sharply that such a rationale would suggest that the Court should overrule cases "going all the way back to the founding."

Appealing to that skepticism, Collins' attorney closed his arguments by cautioning the justices that "the automobile exception is literally knocking at the door of the house."