What is the test for warrantless entry and search?

Defendant relies on Horack v. Superior Court (1970) 3 Cal.3d 720, 91 Cal.Rptr. 569, 478 P.2d 1 for the proposition that lights and loud music inside a residence when no one answers the door are not enough to permit a warrantless entry and search. In Horack the officer received a call that two " 'hippie-type' " individuals had entered what the caller believed was a vacant house. The officer went to the house around 1 p.m. and knocked. He could see there were no furnishings in the house except a stereo which was playing loudly. No one responded to his knocks, and he heard no other sounds from within. The front door was locked. The back door was unlocked, and the officer entered to " 'ascertain if there were people in the dwelling that did not have the authority to be inside.' " (Id. at p. 723, 91 Cal.Rptr. 569, 478 P.2d 1.) The court found the search to be unreasonable.