The knock-and-announce rule requires police officers serving an arrest warrant or a search warrant to knock on the door of a private residence and announce the reason for their presence, rather than forcing their way in. This rule generally requires police officers to wait a reasonable amount of time for the persons inside the residence to respond to the knock at the door and allow the police officers inside.

If the person(s) inside the residence do not respond and allow the police inside within a reasonable amount of time, the police may force themselves inside—by breaking down the door or its latch or lock mechanism, for example.

No-Knock Situations

The United States Supreme Court has held that a police officer is not required to knock-and-announce if doing so would be unreasonable under the circumstances—if, for example, announcing their presence would be dangerous, futile, or result in the destruction of evidence.

No Exclusionary Rule

The Supreme Court has held that a violation of the knock-and-announce rule by the police does not justify excluding evidence the police may find in searching the home, for example.

Knock-and-Announce Rules in State and Federal Statutes

Although the knock-and-announce rule originated in the common law (also known as court opinions, judicial decisions, or case law) the federal government (18 U.S.C. §3109) and many states (in state statutes) have defined the rule in their statutes. This process of writing the law in a code or statute enacted by the state legislature or the United States Congress is known as codifying the law, because it is made a part of the code or statutes.

A state’s knock-and-announce rule is often located in its statutes governing criminal law and criminal procedure.

In Montana, the knock-and-announce rule is a legal principle that requires law enforcement officers to knock on the door of a residence and announce their presence and purpose before entering to execute an arrest or search warrant. This rule is designed to protect the privacy and safety of individuals inside the residence and to prevent unnecessary damage to property. Montana's adherence to this rule is consistent with the Fourth Amendment of the U.S. Constitution, which protects against unreasonable searches and seizures. However, there are exceptions to this rule, such as when officers have a reasonable suspicion that knocking and announcing their presence would be dangerous, futile, or lead to the destruction of evidence. In such no-knock situations, officers may enter without announcing. It's important to note that the U.S. Supreme Court has ruled that evidence obtained in violation of the knock-and-announce rule is not necessarily excluded from court proceedings. This means that even if law enforcement officers fail to follow the knock-and-announce requirement, the evidence they collect may still be admissible. In Montana, the specifics of the knock-and-announce rule and its exceptions would be detailed within the state's statutes governing criminal law and criminal procedure.