Police officers generally need a warrant before they may enter private homes. An exception to this rule is that police may enter a home without a warrant to provide emergency aid to someone inside. This case presents the question of how certain police officers must be that an emergency exists before they are allowed to exercise this authority and enter homes without permission or a warrant. The question is important because police officers carry deadly weapons, are charged with acting upon any potential lawbreaking that they observe, and may use lethal force when they perceive threats to their safety. Allowing police to forcibly enter homes with less than probable cause that an emergency exists would therefore put lives at risk and invite pretextual home entries that are not truly motivated by any need to provide emergency aid. 

In this case, police officers entered William Case’s home without a warrant based on a report that he might want to harm himself. Soon after entering, however, the police shot him. Case maintained that the officers’ warrantless entry into his home violated the Fourth Amendment, but the Montana Supreme Court disagreed. It held that police need only “reasonable suspicion” of an emergency, not the higher standard of “probable cause,” to enter homes without warrants. The U.S. Supreme Court agreed to review this decision, and in August 2025, CAC filed an amicus brief in support of Case.  

Our brief explains that using a standard below probable cause to allow warrantless home entries by police would be contrary to the Fourth Amendment’s text and history. 

First, the common law that was in place when the Fourth Amendment was adopted required more than probable cause, not less, for warrantless home entries. The Supreme Court has held that Founding-era common law rules provide a “baseline” for what is reasonable under the Fourth Amendment. And the common law did not allow law enforcement officers, under any circumstances, to enter homes without warrants to provide emergency aid. Instead, the common law regarded a person’s home as their castle, allowing warrantless entry in only three narrowly defined scenarios. All three scenarios required more than probable cause. Officers, for instance, could enter homes to stop violent “affrays,” but only if they were certain that an affray was occurring because they could perceive it with their own senses.  

Second, the Fourth Amendment’s chief purpose was to restrain discretionary government searches of the home. The Amendment built upon the common law’s respect for the home’s sanctity, and it was largely designed to prevent the kind of arbitrary and intrusive home searches that the Founding generation suffered under British rule—namely, searches conducted under “general warrants” that were not based on sworn evidence or individualized suspicion. The Amendment enshrines in our national charter the Framers’ opposition to searches of the home that are conducted without particularized suspicion backed by reliable evidence. 

Finally, the Framers viewed the requirement of probable cause as a vital safeguard against unfounded searches and seizures. While the Fourth Amendment mentions probable cause only in describing the criteria to obtain a warrant, the Framers understood that standard to be a more general safeguard against all unreasonable searches and seizures, whether or not conducted with a warrant. Given the home’s special status under the common law and in the Fourth Amendment’s history, the Framers would not have sanctioned warrantless home entry based on anything less than probable cause.