The Supreme Court of the United States held that the common law ,"knock and announce" rule was an indispensable component of the Fourth Amendment's "reasonableness" requirement, and therefore, should not be subject to a per se blanket exception.
Richards v. Wisconsin, 117 S. Ct. 1416 (1997).
Constitutional Law - Criminal Procedure - Fourth Amendment - "Knock and Announce" Rule,
Duq. L. Rev.
Available at: https://dsc.duq.edu/dlr/vol36/iss4/14