In a protective sweep, can a search warrant be used to search a person's home without a warrant?

We have independently examined the record. We conclude that the district court did not err in finding that the protective sweep's scope was proper and that the evidence seized was in "plain view." See United States v. McConney, 728 F.2d 1195, 1204-05 (9th Cir.1984) (the presence of exigent circumstances is reviewed de novo ), cert. denied, 469 U.S. 824 (1984). Exigent circumstances permit officers to conduct a protective search when officers have arrested a person inside a residence and "the officers reasonably believe that there might be other persons on the premises who could pose some danger to them." United States v. Gardner, 627 F.2d 906, 909-10 (9th Cir.1980) (footnote omitted).