Sniffer dogs

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, 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 dogs that work to find 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. 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; however, they're also used as a valuable research tool for wildlife biologists. In California, detection dogs are trained to discover quagga mussels on boats at public boat ramps because they are a harmful invasive species for the environment. Detection dogs also tend to be employed for the purposes of finding and collecting the feces of a diverse array of species, including caribou,black-footed ferret, killer whale, and Oregon spotted frog. This process is known as wildlife scat detection.

Detection dogs are also seeing use in the medical industry, as studies have revealed that canines are able to detect specific odours associated with numerous medical conditions, such as cancer.

...
Wikipedia