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, 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 human remains detection dogs (sometimes called cadaver dogs), trained to detect human remains. They are also used for drug raids to locate the drugs in question. Some prisons have dogs trained to detect illicit mobile phones in prison cells.
In recent years, detection dogs have emerged as a valuable research tool for wildlife biologists. In California, they are trained to detect the quagga mussel on boats at public boat ramps, as it is an invasive species. Sniffer dogs have also been enlisted to find bumblebee nests. The Bumblebee Conservation Trust has trained an English Springer Spaniel to detect the colonies, assisting them with the conservation of threatened species. Other studies have employed detection dog for the purposes of finding and collecting the scat of diverse species including caribou, black-footed ferret, killer whales, and Oregon spotted frog.
The dogs are trained to dig or sit when they smell drugs, which triggers automobile searches. But a Tribune analysis of three years of data for suburban departments found that only 44 percent of those alerts by the dogs led to the discovery of drugs or paraphernalia.