The police and other law enforcement (airport security, border patrol) use trained dogs with extraordinary scent detection capabilities to identify illegal narcotics and explosives in motor vehicles and luggage, for example. Whether a dog sniff inspection of such things or places constitutes a search or seizure under the Fourth Amendment to the United States Constitution depends on whether the owner of the personal or real property has a reasonable expectation of privacy that is invaded by the inspection.

The U.S. Supreme Court has held that a dog sniff inspection in public places—such as the exterior of a motor vehicle stopped for a traffic violation or luggage at the airport—does not implicate legitimate privacy interests in the interior of the motor vehicle compartment (trunk, etc.) or luggage. See Illinois v. Caballes, 543 U.S. 405, 409 (2005); United States v. Place, 462 U.S. 696, 707 (1983).

This is because a person does not have the same reasonable expectation of privacy in public places such as a roadway or airport—in which a person must reasonably expect some government intrusion—as in their home, in which a person has a more complete reasonable expectation of privacy. For this reason, a warrantless dog sniff of the exterior of a person’s home would generally violate a person’s reasonable expectation of privacy under the Fourth Amendment.

In permitting warrantless dog sniff searches of the exterior of a motor vehicle and of luggage at the airport, the Supreme Court reasoned that although a person possesses a Fourth Amendment privacy interest in the contents of a motor vehicle trunk or personal luggage, a canine sniff by a well-trained narcotics detection dog does not require opening the luggage. Such a dog sniff inspection does not expose noncontraband items that would otherwise remain hidden from public view—a stark contrast to an officer's rummaging through the contents of the motor vehicle trunk or luggage.

Thus, the manner in which information is obtained through a dog sniff inspection is much less intrusive than a typical search, as the dog sniff discloses only the presence or absence of narcotics, explosives, or other contraband items. Thus, despite the fact that the dog sniff tells the authorities something about the contents of the luggage, the information obtained is limited, and this limited disclosure also ensures that the owner of the property is not subjected to the embarrassment and inconvenience of more intrusive investigations and searches.

In Alaska, as in other states, the use of trained dogs by law enforcement to detect illegal narcotics and explosives in public places like the exteriors of motor vehicles during traffic stops or luggage at airports is considered to not violate the Fourth Amendment. This is based on U.S. Supreme Court rulings, such as Illinois v. Caballes and United States v. Place, which have established that such dog sniff inspections do not implicate legitimate privacy interests because they do not expose noncontraband items and are less intrusive than traditional searches. A person does not have the same reasonable expectation of privacy in public places as they do in their home. Therefore, while a warrantless dog sniff of a home's exterior would generally violate the Fourth Amendment, the same is not true for vehicle exteriors or luggage in public spaces. The dog sniff reveals only the presence or absence of contraband, which limits the scope of the intrusion and the potential embarrassment or inconvenience to the individual.