Can a police officer who stops a motorist for a traffic violation have a police dog sniff around the car for illegal substances such as drugs?
The United States Supreme Court has ruled that people do not have a "reasonable expectation" of privacy in the smell of one's automobile (or one's luggage). For that reason, police use of a sniffer dog does not constitute a search. In other words, even if a police officer has no reason to believe that a car contains an illegal substance, the officer can use a trained “sniffer dog” to check for illegal substances. Any illegal substances that the officer finds with the dog’s help can be used against the motorist at trial (Illinois v. Caballes, U.S. Sup. Ct. 2005). But, the police can't unreasonably prolong traffic stops in order to conduct dog sniffs—see Traffic Stops and Police Dog Sniffs.
by: Paul Bergman