If all goes well, we may end up with a little more Fourth Amendment here in the USA. The Supreme Court is currently considering reviewing a case that will more clearly define what Fourth Amendment implications cops' four-legged friends bring to the (search) party.
A Minnesota state supreme court case (Edstrom v. Minnesota [PDF]) dealing with a K-9's door sniff in an apartment hallway is up for review by the nation's highest court. The state court found in favor of the government, stating that a K-9 sniff only needs reasonable suspicion to comply with the Fourth Amendment and state's own Constitution.
Should we expect a higher standard for dog sniffs? One would think so, considering cops already refer to K-9s as "probable cause on four legs." The Supreme Court recognized in the Rodriguez decision that artificially prolonging pretextual traffic stops solely for the purpose of developing probable cause -- in many cases waiting for a drug dog to arrive at the stop -- violated the Fourth Amendment.
More captive audiences -- residents in their own homes -- shouldn't be treated to a lower standard just because they're never technically "free to go." An apartment resident can't demand officers leave publicly-accessible areas and they certainly can't just pack up their place and leave just because law enforcement doesn't have probable cause to perform a search. But officers can troll hallways with drug dogs based on only the hunch that something illegal may be occurring out of sight.
Drug dogs are trained to do only one thing: detect the odor of drugs. When they alert, officers then have probable cause to effect a search of residence. Limited searches then can be performed without a warrant under the theory that evidence may be destroyed if the residence is not secured while a warrant is obtained.
The home is supposed to be afforded the utmost in Fourth Amendment protections. But when a drug dog is involved, much of that heightened protection dissipates, replaced with non-verbal statements from an animal that can easily be triggered by nothing more than the dog's desire to please its handler. You can't cross-examine a dog to determine its trustworthiness or state of mind. All you can do is hope there's enough failure on the record to call into question the sniff's veracity and that sort of evidence is almost impossible to obtain.
Whether or not the Supreme Court decides to take this case largely depends on how the justices feel about the Jardines decision. In 2013, the Court ruled that taking a drug dog onto a person's porch to sniff for drugs was a search under the Fourth Amendment. But a lot of that reasoning relies on the definition of curtilage. For distinct homes, the privacy begins at the end of the driveway -- something further defined in 2018's Collins decision. In that case, the court held that the Fourth Amendment was violated when the officer entered an open carport to look at an allegedly stolen motorcycle.
But curtilage isn't so easily defined in shared spaces like apartment buildings. Officers can traverse halls just like residents can, provided the common spaces aren't otherwise secured with keypads or card entry. And if they can be in the hall, they can certainly take their dogs in with them. This is gray area the court hasn't directly addressed, and if it refuses to do so in this case, it allows the Fourth Amendment to be applied unequally. Zero protection for common areas that provide access to residents' doors (and their residences beyond) makes the Fourth Amendment a rich (or richer) man's protection, leaving those unable to purchase or rent their own home subject to the whims of police officers and their dogs.