Fourth Amendment jurisprudence includes a concept known as "knock and talk." The rule allows officers to approach a residence and knock on a door in order to talk with the residents (hopefully), just as any private citizen might. And officers can do this even if they are in search of evidence or otherwise investigating a crime. The "knock and talk" is not even a search, according to the Supreme Court.
At least when officers knock on the front door. Perhaps it is a search (of the home's curtilage), and an unreasonable one at that, when officers knock on some other door. That was the conclusion reached by the Third Circuit in a 1983 action just this year. But earlier this week, the Supreme Court, in a per curiam opinion, undid that decision, holding that this "front door" requirement was not "clearly established." The case is Carroll v. Carman. Because of the procedural posture of the case (whether officers were entitled to qualified immunity in a civil suit), the Court went no further than its "not clearly established" holding. It did not, for instance, hold that officers can, in fact, knock on some other door. The which-door-do-I-knock-on conundrum continues.
Sort of. In its decision, the Court notes that quite a few courts of appeals (and even a state supreme court) disagree with the Third Circuit and allow an officer to "knock and talk" on any door that is open to visitors (whatever that means). Although the Court did not cite to the Tenth Circuit, alas, it very well could have. Not all that long ago, the Tenth Circuit upheld a "knock and talk" at the back door of a residence where officers "used the normal route of access" to the door.
We take away two things from SCOTUS's ambivalent decision in Carroll: if you have a not-front-door "knock and talk," consider: (1) how the officer arrived at the door (was it via the "normal route" or some other route); and (2) whether the door was accessible to the public (or "open to visitors"). If either answer (or both) favors your client (not a normal route, or an inaccessible door), then move to suppress on that basis. If neither answer does you any good, consider preserving the legality of the "knock and talk" based on what might be a conflict in the Circuits on this issue.