What is the test for warrantless searches under the Fourth Amendment?

In People v. Duncan (1986) 42 Cal.3d 91, 97, 227 Cal.Rptr. 654, 720 P.2d 2, which also involved warrantless entry into a home, we explained the exception to the Fourth Amendment for searches under exigent circumstances. "We have defined 'exigent circumstances' to include 'an emergency situation requiring swift action to prevent imminent danger to life or serious damage to property....' [Citation.] The action must be 'prompted by the motive of preserving life or property and [must] reasonably appear[ ] to the actor to be necessary for that purpose.' [Citation.]