That principle renders this case a straightforward one. The officers were gathering information in an area belonging to Jardines and immediately surrounding his house— in the curtilage of the house, which we have held enjoys protection as part of the home itself. And they gathered that information by physically entering and occupying the area to engage in conduct not explicitly or implicitly permitted by the homeowner

We therefore regard the area “immediately surrounding and associated with the home”—what our cases call the curtilage—as “part of the home itself for Fourth Amendment purposes".... That principle has ancient and durable roots. Just as the distinction between the home and the open fields is “as old as the common law",....so too is the identity of home
and what Blackstone called the “curtilage or homestall,” for the “house protects and privileges all its branches and appurtenants.” 4 W. Blackstone, Commentaries on the Laws of England 223, 225 (1769). This area around the home is “intimately linked to the home, both physically
and psychologically,” and is where “privacy expectations are most heightened.” California v. Ciraolo, 476 U. S. 207, 213 (1986).

While the boundaries of the curtilage are generally “clearly marked,” the “conception defining the curtilage” is at any rate familiar enough that it is “easily understood from our daily experience.” Oliver, 466 U. S., at 182, n. 12. Here there is no doubt that the officers entered it: The front porch is the classic exemplar of an area adjacent to the home and “to which the activity of home life extends.”


Since the officers’ investigation took place in a constitutionally protected area, we turn to the question of whether it was accomplished through an unlicensed physical intrusion.1 While law enforcement officers need not “shield their eyes” when passing by the home “on public thoroughfares,” Ciraolo, 476 U. S., at 213, an officer’s leave to gather information is sharply circumscribed when he steps off those thoroughfares and enters the Fourth Amendment’s protected areas. In permitting, for example, visual observation of the home from “public navigable airspace,” we were careful to note that it was done “in a physically nonintrusive manner.”....

“Our law holds the property of every man so sacred, that no man can set his foot upon his neighbour’s close without his leave.” 2 Wils. K. B., at 291, 95 Eng. Rep., at 817. As it is undisputed that the detectives had all four of their feet and all four of their companion’s firmly planted on the constitutionally protected extension of Jardines’ home, the only question is
whether he had given his leave (even implicitly) for them to do so. He had not.

“A license may be implied from the habits of the country,” notwithstanding the “strict rule of the English common law as to entry upon a close.” McKee v. Gratz, 260 U. S. 127, 136 (1922) (Holmes, J.). We have accordingly recognized that “the knocker on the front door is treated as an invitation or license to attempt an entry, justifying ingress to the home by solicitors, hawkers and peddlers of all kinds.” Breard v. Alexandria, 341 U. S. 622, 626 (1951). This implicit license typically permits the visitor to approach the home by the front path, knock promptly, wait briefly to be received, and then (absent invitation to linger longer) leave. Complying with the terms of that traditional invitation does not require fine-grained legal knowledge; it is generally managed without incident by the Nation’s Girl Scouts and trick-or-treaters.2 Thus, a police officer not armed with a warrant may approach a home and knock, precisely because that is “no more than
any private citizen might do.”

But introducing a trained police dog to explore the area around the home in hopes of discovering incriminating evidence is something else. There is no customary invitation to do that. An invitation to engage in canine forensic investigation assuredly does not inhere in the very act of hanging a knocker. To find a visitor knocking on the door is routine (even if sometimes unwelcome); to spot that same visitor exploring the front path with a metal detector, or marching his bloodhound into the garden before saying hello and asking permission, would inspire most of us to—well, call the police. The scope of a license—express or implied—is limited not only to a particular area but also to a specific purpose. Consent at a traffic stop to an officer’s checking out an anonymous tip that there is a body in the trunk does not permit the officer to rummage through the trunk for narcotics. Here, the background social norms that invite a visitor to the front door do not invite him there to conduct a search.