In Wilson v. Arkansas, 514 U.S. 927 (1995), we held that the Fourth Amendment incorporates the common law requirement that police officers entering a dwelling must knock on the door and announce their identity and purpose before attempting forcible entry.
[. . .] In order to justify a "no knock" entry, the police must have a reasonable suspicion that knocking and announcing their presence, under the particular circumstances, would be dangerous or futile, or that it would inhibit the effective investigation of the crime by, for example, allowing the destruction of evidence. This standard--as opposed to a probable cause requirement--strikes the appropriate balance between the legitimate law enforcement concerns at issue in the execution of search warrants and the individual privacy interests affected by no knock entries. Cf. Maryland v. Buie, 494 U.S. 325, 337 (1990) (allowing a protective sweep of a house during an arrest where the officers have "a reasonable belief based on specific and articulable facts that the area to be swept harbors an individual posing a danger to those on the arrest scene"); Terry v. Ohio, 392 U.S. 1, 30 (1968) (requiring a reasonable and articulable suspicion of danger to justify a pat down search). This showing is not high, but the police should be required to make it whenever the reasonableness of a no knock entry is challenged. Richards v. Wisconsin, 520 US 385 (1997)Knock-and-announce rule
Knock-and-announce rule: an overview
Under the common law knock-and-announce rule, a police officer executing a search warrant generally must not immediately force his or her way into a residence. Instead, he or she must first knock, identify himself or herself and his or her intent, and wait a reasonable amount of time for the occupants to let him or her into the residence. The Supreme Court has held that the knock-and-announce rule forms part of a judge's inquiry into the reasonableness of a search under the Fourth Amendment. See Wilson v. Arkansas, 514 U.S. 927 (1995).
The Supreme Court identified several reasons supporting the rule in Hudson v. Michigan, 547 U.S. 586 (2006). These include preventing accidental injuries to officers and occupants, limiting property damage, and protecting occupants' privacy and dignity. This rule, however, does not protect occupants from government seizure of their property. Accordingly, although the exclusionary rule may apply to some police violations of the rule, it does not apply to all.
A police officer is not required to knock and announce if doing so would be unreasonable, e.g. if there is a risk of injury to the police officer executing the search warrant or a risk of the occupants destroying the sought-after evidence between the police officer's knock and his or her entry. The applicability of this exception is determined on a case-by-case basis. For example, in Richards v. Wisconsin, 520 U.S. 358 (1997), the Supreme Court held that there is no blanket exception to the knock-and-announce rule for searches in felony drug cases. Officers may, however, seek a "no-knock" warrant in advance if they suspect that a no-knock entry will be justified when they serve the warrant.
In practice, over the past decade, police officers have increasingly relied on no-knock warrants, particularly in drug cases and especially in major cities. There has been a corresponding increase in the number of innocent persons accidentally injured or killed by police officers executing no-knock warrants.
Illustrative caselaw
See, e.g. Hudson v. Michigan, 547 U.S. 586 (2006).
