Can a law enforcement officer enter a person's home without a warrant?

One exception to the warrant requirement is "the need to assist persons who are seriously injured or threatened with such injury. ' "The need to protect or preserve life or avoid serious injury is justification for what would be otherwise illegal absent an exigency or emergency." ' [Citations.] Accordingly, law enforcement officers may enter a home without a warrant to render emergency assistance to an injured occupant or to protect an occupant from imminent injury. [Citations.]" (Brigham City v. Stuart (2006) 547 U.S. 398, 403 (Brigham).) "This 'emergency aid exception' does not depend on the officers' subjective intent or the seriousness of any crime they are investigating when the emergency arises. [Citation.] It requires only 'an objectively reasonable basis for believing,' [citation], that 'a person within [the house] is in need of immediate aid,' [citation]." (Michigan v. Fisher (2009) 558 U.S. 45, 47 (Michigan).) "Officers do not need ironclad proof of 'a likely serious, life-threatening' injury to invoke the emergency aid exception." (Id. at p. 49.) " '[A]n objectively reasonable basis for believing' that medical assistance was needed, or persons were in danger" suffices. (Ibid.)