To search your house, police generally need a search warrant (there are exceptions to this requirement) based on probable cause.
But while the overwhelming majority of juice arrests occur during transactions (receiving or selling), anything can happen. For example, I saw a guy busted when he got rough with his girlfriend, the police responded, and she pointed out his stash just to get even. I once represented a guy who got busted when a fire started in his house (when he wasn't home) and the firefighters saw drugs and called the police. Cases like these are few and far between, of course, but like Rutger Hauer said in the movie "Nighthawks": "There is no security."