A dog sniff inspection can be helpful in investigations because trained dogs are sensitive to smells and can identify suspicious objects more easily than humans. Whether a dog sniff inspection constitutes a search or seizure under the Fourth Amendment depends on whether there is a reasonable expectation of privacy intruded by the inspection. Dog-sniff inspection of items in public does not constitute a search or a seizure under the Fourth Amendment so long as the dog is lawfully present at the scene and the conduct is proper. Following this principle, inspection of containers, packages, lockers or vehicle exteriors can be properly conducted without a warrant or probable cause.
A dog sniff inspection has been held as a Fourth Amendment search when a person expects the place or property being inspected to be free of governmental intrusion. For example, a dog sniff of someone’s home may be considered a search.