Can a police officer enter a house without waiting for a reply?

After knocking and announcing their presence, the officers were able to enter the house immediately without waiting for a reply under the "exigent circumstance" exception to the statute. United States v. McConney, 728 F.2d 1195, 1199 (9th Cir.) (en banc), cert. denied, 469 U.S. 824 (1984); United States v. Whitney, 633 F.2d 902, 908 (9th Cir.1980), cert. denied, 450 U.S. 1004 (1981). Exigent circumstances are those which "would cause a reasonable person to believe that entry ... was necessary to prevent physical harm to the officers or other persons, the destruction of relevant evidence, the escape of the suspect, or some other consequence improperly frustrating legitimate law enforcement efforts." McConney, 728 F.2d at 1199.