From 2021 until 2026, the U.S. Supreme Court did not decide one case involving traditional Fourth Amendment issues—such as what is a search, when is a warrant required and whether the exclusionary rule applies.

I taught Criminal Procedure - Investigations in the fall semester and struggled to explain to my students why the justices seemingly had lost interest in the Fourth Amendment. But this term, there are two Fourth Amendment cases, one already decided and one to be argued this spring.

Case v. Montana

The Supreme Court long has stressed that the home is special under the Fourth Amendment and that generally a warrant is required for the police to enter someone’s house to search or arrest. But there are exceptions to the warrant requirement. One of these is exigent circumstances that allow police to enter without a warrant if an emergency justifies doing so.

In Brigham City v. Stuart (2006), the Supreme Court held that police could enter a home without a warrant if they had an objectively reasonable belief that someone is seriously injured or imminently threatened with injury. The police in Brigham City, Utah, had received a call about a loud party. When they arrived at the house, officers saw two teenagers in the backyard drinking beer. They also saw, through a screen door and window, that there was a fight in the kitchen between four adults and a teenager. The police entered the house without a warrant.

The officers then arrested the adults in the house and charged them with contributing to the delinquency of a minor, disorderly conduct and intoxication. At trial, the defendants filed a motion to suppress all evidence obtained after the officers entered the home, arguing that the officers’ warrantless entry violated the Fourth Amendment. The court granted the motion, and the Utah Court of Appeals affirmed, ruling that any evidence gained at that time had to be excluded.

But the U.S. Supreme Court reversed. Chief Justice John Roberts wrote the opinion for the court and explained: “In these circumstances, the officers had an objectively reasonable basis for believing both that the injured adult might need help and that the violence in the kitchen was just beginning. Nothing in the Fourth Amendment required them to wait until another blow rendered someone ‘unconscious’ or ‘semi-conscious’ or worse before entering.”

Case v. Montana, decided Jan. 14, reaffirmed the court’s holding in Brigham City v. Stuart: Police may enter a home without a warrant if they have an objectively reasonable basis for believing someone needs emergency assistance. William Case’s ex-girlfriend called the police and told them that Case had spoken of committing suicide. The police officers were familiar with Case and that he had a history of alcohol abuse and mental health issues. They knew that he had previously threatened suicide and that he had once seemed to attempt “suicide-by-cop” by confronting the police in a way that was likely to provoke a lethal response.

The officers went to Case’s house and knocked on the doors and yelled into an open window. They got no response. Peering through the window, they saw an empty gun holster and a notepad, which was consistent with the police having been told that Case had written a suicide note.

The officers waited for the chief of police to arrive, and about 40 minutes after first arriving, they decided to enter the house. When the officers did so, they announced their presence but got no response. The officers found Case in a closet. He was holding a black object that looked like a gun, and the police officer who saw this shot Case. He was seriously wounded but survived. The officers then found a handgun in a laundry basket near the closet where Case had been.

Case moved to suppress all of the evidence that police gained from his house. He said that the police violated the Fourth Amendment by entering his home without a warrant. The Montana courts ruled against Case. The Supreme Court granted certiorari to decide whether there has to be probable cause to believe that an occupant is in peril to justify entering a home without a warrant.

The Supreme Court unanimously held that probable cause is not required. Rather, the court affirmed the standard from Brigham City v. Stuart that police may enter a home without a warrant when there is an objectively reasonable basis to believe that a person in a home is in peril.

Justice Elena Kagan wrote for the court and declared: “The officers had, as Brigham City requires, an ‘objectively reasonable basis for believing” that their intervention was needed to prevent serious harm.” The court concluded: “We repeat today what we have held before: An officer may enter a home without a warrant if he has ‘an objectively reasonable basis for believing that an occupant is seriously injured or imminently threatened with such injury.’”

Case v. Montana thus does not make new law or change the legal standard under the Fourth Amendment, though it does reject the approach taken by some lower courts that have said that there had to be probable cause of a danger to justify warrantless entry of a home.

Chatrie v. United States

The other Fourth Amendment case this term, Chatrie v. United States, promises to be more significant—if nothing else because it raises an issue never before addressed by the Supreme Court: Is police use of a geofence (a method of location tracking) considered a search within the meaning of the Fourth Amendment?

A geofence warrant allows law enforcement to obtain from the cellular service provider the identities of cellphones that were in the vicinity of a particular location at a specific time. Cellphones and similar devices are constantly and automatically connecting to cell towers. It is thus possible through this location information to determine where a cellphone was at a particular point in time.

In this case, the police obtained and served on Google a geofence warrant seeking a list of every device within 150 meters of the location of a bank robbery within one hour of the robbery. After Google complied with this, the police asked for information about the location of some specific devices over a two-hour period. Although the police did not get another warrant, Google provided this information and also identified the subscriber information for three of the devices. One of these devices belonged to Okello Chatrie. Based on the evidence derived from Google, Chatrie was convicted of armed robbery.

The Richmond, Virginia-based 4th U.S. Circuit Court of Appeals, in a 2-1 decision, ruled the geofence was not a search within the meaning of the Fourth Amendment. The Fourth Circuit granted en banc review, and in a one-sentence per curiam opinion affirmed the district court’s decision. The court was divided 7-7 on whether a Fourth Amendment search had occurred, with one judge declining to reach the issue. Of the seven judges who found a violation of the Fourth Amendment, six concluded that evidence should not be excluded because of the good-faith exception to the exclusionary rule.

The Supreme Court granted certiorari only on the issue of whether the execution of the geofence warrant violated the Fourth Amendment. This is an issue where there is a split among the federal courts of appeals. The high court did not grant certiorari on the other issue presented, which was “whether the exclusionary rule should apply to the evidence derived from the geofence warrant.”

This will be the Supreme Court’s second major case about cellular location information. In Carpenter v. United States (2018), the court ruled that it was a search under the Fourth Amendment, and thus required a warrant based on probable cause, for police to obtain 127 days of cellular location information from a person’s service provider. The court, in a 5-4 decision, expressly rejected the government’s argument that there was not a search because the defendant had voluntarily shared this information with a third party—his cellular provider.

Lower courts have struggled with many issues in applying Carpenter. How much information must police acquire in order for it to be considered a search? What technology does it apply to? What are the limits to the third-party doctrine, which says that there is no reasonable expectation of privacy for information that a person shares with a third party?

Chatrie v. United States will be the court’s first case since Carpenter to deal with cellular location information. It is notable that the composition of the court has changed since Carpenter. The decision was 5-4, with Roberts’ majority opinion being joined by Justices Ruth Bader Ginsburg, Stephen Breyer, Sonia Sotomayor, and Kagan. Each of the four dissenters—Justices Anthony Kennedy, Clarence Thomas, Samuel Alito, and Neil Gorsuch—wrote a separate opinion. Might the current court, especially with Justice Amy Coney Barrett replacing Justice Ginsburg, call Carpenter into question? Or might the court reaffirm it and extend it to geofences?

Whatever the court decides is sure to matter for the many issues arising from police using new technology and when its use is considered a search within the meaning of the Fourth Amendment. The case will be argued this spring and decided by the end of June.

Erwin Chemerinsky is dean of the University of California at Berkeley School of Law. He is an expert in constitutional law. He’s also the author of many books, including his most recent ones: Campus Speech and Academic Freedom: A Guide for Difficult Times and The Supreme Court October Term 2024: Taking Sides.