A detection dog or sniffer dog is a dog that is trained to use its senses to detect substances such as explosives, illegal drugs, wildlife scat, semen, currency, blood, and contraband electronics, such as illicit mobile phones. The sense most used by detection dogs is smell. Hunting dogs that search for game, and search and rescue dogs that work to find missing humans are generally not considered detection dogs but fit instead under their own categories. There is some overlap, as in the case of cadaver dogs, trained to search for human remains.
A police dog is essentially a detection dog that is used as a resource, for police in specific scenarios such as conducting drug raids, finding missing criminals, and locating stashed currency. Frequently, detection dogs are thought to be used for law enforcement purposes. Experts say that dog-sniff evidence should not be used in the criminal justice system, pointing to wrongful convictions, human biases that skew animal behavior, and the lack of systematic research into what dogs detect or how they do it.