The U.S. Supreme Court ruled on March 26,2013 in Florida v. Jardines (http://www.supremecourt.gov/opinions/12pdf/11-564_5426.pdf )
that the use of a drug-sniffing dog to investigate the front door of a home was a “search” within the meaning of the Fourth Amendment. Thankfully, the Supreme Court ruled this way – or we’d have police trolling apartment complexes, buildings, public spaces, etc with an army of intrusive sniffing dogs. The justices ruled that having a dog sniffing at one’s door was indeed a search, and thus subject to the limitations of the Fourth Amendment.
Whether a police officer bringing a drug dog to sniff the door to a residence constitutes “trespassing” is an interesting issue brought up in this case. We will see how this court’s ruling will be played out as time progresses. The court found it unnecessary to determine whether the officers violated Jardines’ “reasonable expectation of privacy”, instead they focused on whether the officers’ physical intrusion on the porch established that the search had occurred.