A detection dog or sniffer dog is a dog that is trained to and works at using its senses (almost always the sense of smell) to detect substances such as explosives, illegal drugs, wildlife scat, currency, or blood. Hunting dogs that search for game and search dogs that search for missing humans are generally not considered detection dogs. There is some overlap, as in the case of cadaver dogs, trained to search for human remains. Some police dogs that are used in drug raids are trained not only to locate narcotics, but also persons who may be hiding from the police, as well as stashed currency. Some detector dogs can locate contraband electronics, such as illicit mobile phones in prisons.