These dogs are amazing. A sniffer dog's sense of smell is 2000 times more sensitive than that of humans.
They can detect explosives, illegal drugs, or blood.
Hunting dogs that search for game and search dogs that search for missing humans are generally not considered detection dogs, but, as in the case of human remains detection dogs (sometimes called cadaver dogs), trained to detect human remains.
In the state of California, dogs are trained to detect the Quagga Mussel on boats at public boat ramps, as it is a invasive species.
Sniffer dogs have also been enlisted to find bumblebee nests. The Bumblebee Conservation Trust has trained a springer spaniel to detect the colonies, assisting them with the conservation of threatened species.
Some prisons have dog trained to detect contraband cell phones in prison cells!
Detection dogs have been trained to search for many substances, including:
Plants, animals, produce and other agricultural items
Polycarbonate optical discs such as DVDs - used to search for bootleg recordings
Expired food items
Mobile phones as contraband in prisons
One notable quality of detection dogs is that they are able to discern individual scents even when the scents are combined or masked by other odours.
In one case at an Australian prison, a detection dog foiled an attempt to smuggle drugs that had been hidden in a woman's bra and smeared with coffee, pepper and Vicks Vapo-rub!
They can even detect things (blood, etc.) that have been left for as long as 10 years. They can detect blood even if it has been scrubbed off surfaces. In one case, a sniffer dog sniffed a drop of blood on the wall that had been attempted to be scrubbed off!