What is the impact of the knock and announce requirement for police officers to enter a person's home?

But the protection offered by the Fourth Amendment and by our law does not exhaust itself once a warrant is obtained. The concern for the privacy, the safety, and the property of our citizens continues and is reflected in knock and announce requirements. It finds expression in the knock and announce statute which allows an officer to "break open any outer or inner door of a house ... to execute a search warrant if, after notice of his authority and purpose," he is refused admittance. 18 U.S.C. Sec. 3109. Nor should the safety and property "emanations from the core of the fourth amendment" be overlooked by too exclusive a focus on the privacy factor. United States v. Lockett, 919 F.2d 585, 592 (9th Cir.1990) (Fernandez, J., concurring).