Here's a convoluted Fourth Amendment case in which the police found drugs in this guy's apartment after they showed up in connection with the defendant's report that there was a prowler in the area. The police found the drugs by accident, and defendant got nailed.
The case is United States v. Iverson, decided on July 31. This case took place in Western New York. Defendant invited a nice girl into his apartment; he had met her at a liquor store. We all want love, right? But the girl behaved suspiciously, and defendant saw a guy lurking outside the building. After she abruptly left the apartment, believing the girl was a setting up defendant for a robbery, he called the police, who were looking for the prowler who had allegedly robbed a pizza parlor. The police show up at defendant's place after defendant invited them in. Hey, we all want houseguests, right? The lawmen were not there to arrest or search defendant, but his door was open when they were looking for the prowler. The police dog, who had tagged along looking for the prowler's scent, smelled the defendant's drugs, and after some give and take in which the police promised defendant would not get into too much trouble, defendant let the police see the drugs, which got him arrested.
Defendant wants the drugs suppressed as a the product of an unlawful search. But the trial court found, and the Court of Appeals agrees, that the search was not illegal. Defendant gave the police consent to enter his apartment, even if that consent was implied. There is also no evidence the police entered the apartment for purposes of searching defendant; they were looking for the prowler. While defendant claims the police dog's sniffing was an unlawful search, the Supreme Court has already ruled that a "canine sniff" is not a search under the Fourth Amendment. Since the police were lawfully in defendant's apartment and no one commanded the dog to look for drugs, the search was not reasonable.
What do we learn from this? You do not have the let the police into your apartment without a warrant. If you do -- and I know it is hard to say know when the police arrive -- there is a risk the police will find your stash, your gun or whatever else you have closeted away. A police dog can sniff anything out.