This is because it is considered a search. However, there does not need to be any suspicion or probable cause for a drug-sniffing dog to investigate your belongings in a place like an airport. The dogs may sniff your luggage for drugs, explosives, or other prohibited items.

Yes, drug-sniffing dogs (as well as explosives-detection dogs) are a routine part of the "behind-the-scenes" security process for checked luggage at most international and major domestic airports. While passengers usually only see the "K9 units" patrolling the terminal or the customs area, specialized teams work in the secure baggage handling areas where your suitcases are sorted after you drop them at the check-in counter. These dogs are trained to detect the chemical signatures of narcotics, currency, and "agricultural contraband" (like certain fruits or meats that are prohibited from crossing borders). At U.S. airports, the TSA primarily focuses on explosives, but U.S. Customs and Border Protection (CBP) and local law enforcement often use dual-purpose dogs to sweep for drugs in both incoming and outgoing international cargo and baggage. It is a common myth that dogs only sniff "suspicious" bags; in reality, they often conduct "air scenting" in large sorting rooms, allowing them to scan hundreds of bags per hour with remarkable accuracy. If a dog "alerts" on a checked bag, security personnel will typically pull the bag for a manual search, often in the presence of the owner or via a "search notification" tag placed inside the luggage.