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A detection dog or sniffer dog is a
dog The dog (''Canis familiaris'' or ''Canis lupus familiaris'') is a domesticated descendant of the gray wolf. Also called the domestic dog, it was selectively bred from a population of wolves during the Late Pleistocene by hunter-gatherers. ...
that is trained to use its
sense A sense is a biological system used by an organism for sensation, the process of gathering information about the surroundings through the detection of Stimulus (physiology), stimuli. Although, in some cultures, five human senses were traditio ...
s to detect substances such as
explosive An explosive (or explosive material) is a reactive substance that contains a great amount of potential energy that can produce an explosion if released suddenly, usually accompanied by the production of light, heat, sound, and pressure. An ex ...
s,
illegal drug The prohibition of drugs through sumptuary legislation or religious law is a common means of attempting to prevent the recreational use of certain intoxicating substances. An area has a prohibition of drugs when its government uses the for ...
s, wildlife scat, semen, currency,
blood Blood is a body fluid in the circulatory system of humans and other vertebrates that delivers necessary substances such as nutrients and oxygen to the cells, and transports metabolic waste products away from those same cells. Blood is com ...
, and
contraband Contraband (from Medieval French ''contrebande'' "smuggling") is any item that, relating to its nature, is illegal to be possessed or sold. It comprises goods that by their nature are considered too dangerous or offensive in the eyes of the leg ...
electronics such as illicit mobile phones. The sense most used by detection dogs is smell.
Hunting dog A hunting dog is a Dog, canine that hunts with or for hunters. There are several different Dog type, types of hunting dog developed for various tasks and purposes. The major categories of hunting dog include hounds, terriers, cur type dogs, and ...
s that search for
game A game is a structured type of play usually undertaken for entertainment or fun, and sometimes used as an educational tool. Many games are also considered to be work (such as professional players of spectator sports or video games) or art ...
, and
search and rescue dog A search-and-rescue (SAR) dog is a dog trained to respond to crime scenes, accidents, missing persons events, as well as Natural disaster, natural or Disaster, man-made disasters. These dogs detect human scent, which is a distinct odor of skin f ...
s 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 A police dog, also known as a K-9 (phonemic abbreviation of canine), is a dog that is trained to assist police and other law enforcement officers. Their duties may include searching for drugs and explosives, locating missing people, findin ...
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. Although detection dogs are often used for law enforcement purposes, they are also used as a valuable research tool for wildlife biologists. In
California California () is a U.S. state, state in the Western United States that lies on the West Coast of the United States, Pacific Coast. It borders Oregon to the north, Nevada and Arizona to the east, and shares Mexico–United States border, an ...
, detection dogs are trained to discover quagga mussels on boats at public boat ramps because they are a harmful
invasive species An invasive species is an introduced species that harms its new environment. Invasive species adversely affect habitats and bioregions, causing ecological, environmental, and/or economic damage. The term can also be used for native spec ...
for the environment. Detection dogs also tend to be employed for the purposes of finding and collecting the
feces Feces (also known as faeces American and British English spelling differences#ae and oe, or fæces; : faex) are the solid or semi-solid remains of food that was not digested in the small intestine, and has been broken down by bacteria in the ...
of a diverse array of species, including
caribou The reindeer or caribou (''Rangifer tarandus'') is a species of deer with circumpolar distribution, native to Arctic, subarctic, tundra, boreal, and mountainous regions of Northern Europe, Siberia, and North America. It is the only represe ...
, black-footed ferret, killer whale, and Oregon spotted frog. This process is known as wildlife scat detection.


Functions

Detection dogs have been trained to search for many things, both animate and inanimate, including: *
Bed bug Bed bugs are parasitic insects from the genus ''Cimex'', which are micropredators that haematophagy, feed on blood, usually at night. Their bites can result in a number of health impacts, including skin rashes, psychological effects, and aller ...
s *
Cancer Cancer is a group of diseases involving Cell growth#Disorders, abnormal cell growth with the potential to Invasion (cancer), invade or Metastasis, spread to other parts of the body. These contrast with benign tumors, which do not spread. Po ...
*
Currency A currency is a standardization of money in any form, in use or circulation as a medium of exchange, for example banknotes and coins. A more general definition is that a currency is a ''system of money'' in common use within a specific envi ...
(e.g. large amounts of money carried by passengers in airports that should be declared to
customs Customs is an authority or Government agency, agency in a country responsible for collecting tariffs and for controlling International trade, the flow of goods, including animals, transports, personal effects, and hazardous items, into and out ...
) *
Drug A drug is any chemical substance other than a nutrient or an essential dietary ingredient, which, when administered to a living organism, produces a biological effect. Consumption of drugs can be via insufflation (medicine), inhalation, drug i ...
s * Endangered animal species (e.g., black-footed ferret) *
Explosives An explosive (or explosive material) is a reactive substance that contains a great amount of potential energy that can produce an explosion if released suddenly, usually accompanied by the production of light, heat, sound, and pressure. An exp ...
*
Fire accelerant In fire protection, an accelerant or ignitable liquid is any substance or mixture that accelerates or speeds the development and escalation of fire. Accelerants are often used to commit arson, and some accelerants may cause an explosion. Some fi ...
s (e.g.,
arson Arson is the act of willfully and deliberately setting fire to or charring property. Although the act of arson typically involves buildings, the term can also refer to the intentional burning of other things, such as motor vehicles, watercr ...
investigation) *
Firearm A firearm is any type of gun that uses an explosive charge and is designed to be readily carried and operated by an individual. The term is legally defined further in different countries (see legal definitions). The first firearms originate ...
s * Gourmet fungi, such as
truffle A truffle is the Sporocarp (fungi), fruiting body of a subterranean ascomycete fungus, one of the species of the genus ''Tuber (fungus), Tuber''. More than one hundred other genera of fungi are classified as truffles including ''Geopora'', ''P ...
s (e.g. French black truffle (''
Tuber melanosporum ''Tuber melanosporum'', called the black truffle, Périgord truffle or French black truffle, is a species of truffle native to Southern Europe. It is one of the most expensive edible fungi in the world. In 2013, the truffle cost between 1,000 a ...
''), Italian white truffle ('' Tuber magnatum''), chanterelles ('' Cantharellus cibarius''), porcini (''
Boletus edulis ''Boletus edulis'' (English: cep, penny bun, porcino) is a basidiomycete fungus, and the type species of the genus ''Boletus''. It is prized as an edible mushroom. The fungus produces Basidiospore, spore-bearing basidiocarp, fruit bodies ...
''),
morel ''Morchella'', the true morels, is a genus of edible sac fungi closely related to anatomically simpler cup fungi in the order Pezizales ( division Ascomycota). These distinctive fungi have a honeycomb appearance due to the network of ridges ...
s ('' Morchella esculenta''), and other varieties of mushroom. * Human remains *
Invasive species An invasive species is an introduced species that harms its new environment. Invasive species adversely affect habitats and bioregions, causing ecological, environmental, and/or economic damage. The term can also be used for native spec ...
(e.g., quagga mussel) *
Ivory Ivory is a hard, white material from the tusks (traditionally from elephants) and Tooth, teeth of animals, that consists mainly of dentine, one of the physical structures of teeth and tusks. The chemical structure of the teeth and tusks of mamm ...
*
Mobile phone A mobile phone or cell phone is a portable telephone that allows users to make and receive calls over a radio frequency link while moving within a designated telephone service area, unlike fixed-location phones ( landline phones). This rad ...
s (e.g. as
contraband Contraband (from Medieval French ''contrebande'' "smuggling") is any item that, relating to its nature, is illegal to be possessed or sold. It comprises goods that by their nature are considered too dangerous or offensive in the eyes of the leg ...
in prisons) *
Mold A mold () or mould () is one of the structures that certain fungus, fungi can form. The dust-like, colored appearance of molds is due to the formation of Spore#Fungi, spores containing Secondary metabolite#Fungal secondary metabolites, fungal ...
* Plants, animals,
produce In American English, produce generally refers to wikt:fresh, fresh List of culinary fruits, fruits and Vegetable, vegetables intended to be Eating, eaten by humans, although other food products such as Dairy product, dairy products or Nut (foo ...
, and agricultural items that have to go through customs * SIM cards *
Termite Termites are a group of detritivore, detritophagous Eusociality, eusocial cockroaches which consume a variety of Detritus, decaying plant material, generally in the form of wood, Plant litter, leaf litter, and Humus, soil humus. They are dist ...
s *
Diabetes Diabetes mellitus, commonly known as diabetes, is a group of common endocrine diseases characterized by sustained high blood sugar levels. Diabetes is due to either the pancreas not producing enough of the hormone insulin, or the cells of th ...
* USB drives *
Wildlife Wildlife refers to domestication, undomesticated animals and uncultivated plant species which can exist in their natural habitat, but has come to include all organisms that grow or live wilderness, wild in an area without being species, introdu ...
scat Sniffer dogs can be trained to locate small infestations of invasive and non-native weeds. The world's first Spotted Knapweed K-9 detection program successfully completed field-testing for Montana State University in 2004. Upon completion of the testing, Knapweed Nightmare was finding low densities of non-native invasive knapweed rosettes in the field with a 93% overall success rate. She followed it up with 98% in the final trials in open fields, demonstrating that dogs can effectively detect low densities of invasive plants. Detection dogs are able to discern individual scents even when the scents are combined or masked by other odors. In 2002, a detection dog foiled a woman's attempt to smuggle marijuana into an Australian prison in
Brisbane Brisbane ( ; ) is the List of Australian capital cities, capital and largest city of the States and territories of Australia, state of Queensland and the list of cities in Australia by population, third-most populous city in Australia, with a ...
. The marijuana had been inserted into a balloon, which was smeared with
coffee Coffee is a beverage brewed from roasted, ground coffee beans. Darkly colored, bitter, and slightly acidic, coffee has a stimulating effect on humans, primarily due to its caffeine content, but decaffeinated coffee is also commercially a ...
, pepper, and
petroleum jelly Petroleum jelly, petrolatum (), white petrolatum, soft paraffin, or multi-hydrocarbon, CAS number 8009-03-8, is a semi-solid mixture of hydrocarbons (with carbon numbers mainly higher than 25), originally promoted as a topical ointment for i ...
and then placed in her bra.


Bed bug detection dogs

Detection dogs are often specially trained by handlers to identify the scent of
bed bug Bed bugs are parasitic insects from the genus ''Cimex'', which are micropredators that haematophagy, feed on blood, usually at night. Their bites can result in a number of health impacts, including skin rashes, psychological effects, and aller ...
s. With the increased focus on green pest management and
integrated pest management Integrated pest management (IPM), also known as integrated pest control (IPC) integrates both chemical and non-chemical practices for economic control of pests. The UN's Food and Agriculture Organization defines IPM as "the careful consideratio ...
, as well as the increase in global travel and shared living accommodations, bed bugs have become more prevalent. Detecting bed bugs is a complicated process because insects have the ability to hide almost anywhere. Detection dogs help solve this problem because of their size, speed, and sense of smell. Detection dogs use their unique ability to smell in parts per trillion in order to track bed bugs in every phase of their life cycle. They can find bugs in places humans cannot such as wall voids, crevices, and furniture gaps. Dogs are also a safer alternative to pesticide use. If detection dogs can find out exactly where bed bugs are located, they can minimize the area that needs to be sprayed. The National Pest Management Association released their "Bed Bug Best Management Practices" in 2011 which outlines the minimum recommendations regarding not only treatment, but the certification and use of bed bug detection canines. The NPMA's Best Management Practices emphasizes the importance of having bed bug detection dog teams certified by third party organizations who are not affiliated to the trainer or company that sold the canine. Scientists at the
University of Kentucky The University of Kentucky (UK, UKY, or U of K) is a Public University, public Land-grant University, land-grant research university in Lexington, Kentucky, United States. Founded in 1865 by John Bryan Bowman as the Agricultural and Mechanical ...
reviewed studies on bed bug detection dogs and concluded that although expensive for operators, they are a reliable source as long as they undergo the proper training. In another study, detection dogs had a 97.5% correct positive indication rate on identifying bed bugs (''
Cimex lectularius ''Cimex lectularius'', or the common bed bug, is a species of Cimicidae. Its primary hosts are humans, and it is one of the world's major "nuisance pests." Although bed bugs can be infected with at least 28 human pathogens, no studies have fou ...
'') and their eggs – with zero false positives – all while accurately distinguishing them from
carpenter ant Carpenter ants (''Camponotus'' spp.) are a genus of large ants (workers ) indigenous to many parts of the world. True carpenter ants build nests inside wood, consisting of galleries chewed out with their mandibles or jaws, preferably in dead, ...
s,
cockroach Cockroaches (or roaches) are insects belonging to the Order (biology), order Blattodea (Blattaria). About 30 cockroach species out of 4,600 are associated with human habitats. Some species are well-known Pest (organism), pests. Modern cockro ...
es, and
termites Termites are a group of detritophagous eusocial cockroaches which consume a variety of decaying plant material, generally in the form of wood, leaf litter, and soil humus. They are distinguished by their moniliform antennae and the sof ...
. They also successfully differentiated live bed bugs and viable bed bug eggs from dead bed bugs, cast skins, and feces with a 95% correct positive indication rate. Bed bug detection dogs should be certified by a national organization like the World Detector Dog Organization (WDDO) or the National Entomology Scent Detection Canine Association (NESDCA). There are a few independent K9 bed bug inspection companies that have multiple certifications.


Wildlife scat detection

Scat is abundant in the wild and contains valuable data. Wildlife scat detection represents a fairly non-invasive method of study for many species where live-capture once predominated. Compared with other methods of scat collection, dogs are able to survey larger areas in less time at decreased costs. Research shows that detection dogs can find laboratory rats and mice in a large rodent-free area of . Some specific types of feces that detection dogs have had success in identifying include killer whale feces,
northern spotted owl The northern spotted owl (''Strix occidentalis caurina'') is one of three spotted owl subspecies. A western North American bird in the family Strigidae, genus ''Strix (genus), Strix'', it is a medium-sized dark brown owl native to the Pacific N ...
pellets, and
salamander Salamanders are a group of amphibians typically characterized by their lizard-like appearance, with slender bodies, blunt snouts, short limbs projecting at right angles to the body, and the presence of a tail in both larvae and adults. All t ...
s.


COVID-19 detection

Some countries have trained dogs to detect COVID-19. Australia has been using some of these in 2021. Researchers in Paris in March 2022 reported in a preprint not yet peer-reviewed that trained dogs were very effective for rapidly detecting the presence of SARS-Cov2 in people, whether displaying symptoms or not. The dogs were presented with sweat samples to smell from 335 people, of whom 78 with symptoms and 31 without tested positive by PCR. The dogs detected 97% of the symptomatic and 100% of the asymptomatic infections. They were 91% accurate at identifying volunteers who were not infected, and 94% accurate at ruling out the infection in people without symptoms. The authors said "Canine testing is non-invasive and provides immediate and reliable results. Further studies will be focused on direct sniffing by dogs to evaluate sniffer dogs for mass pre-test in airports, harbors, railways stations, cultural activities, or sporting events."


Criticism


Accuracy


Australia

In 2001, the Australian state of
New South Wales New South Wales (commonly abbreviated as NSW) is a States and territories of Australia, state on the Eastern states of Australia, east coast of :Australia. It borders Queensland to the north, Victoria (state), Victoria to the south, and South ...
introduced legislation that granted police the power to use drug detection dogs without a warrant in public places such as licensed venues (venues licensed to serve alcohol),
music festivals A music festival is a festival, community event with music, performances of singing and instrument playing that is often presented with a theme such as musical genre (e.g., rock music, rock, blues, folk music, folk, jazz, classical music), nation ...
, and
public transport Public transport (also known as public transit, mass transit, or simply transit) are forms of transport available to the general public. It typically uses a fixed schedule, route and charges a fixed fare. There is no rigid definition of whic ...
. The law was reviewed in 2006 by the New South Wales Ombudsman, who handed down a critical report regarding the use of dogs for drug detection. The report stated that prohibited drugs were found in only 26% of searches following an indication by a drug sniffer dog. Of these, 84% were for small amounts of
cannabis ''Cannabis'' () is a genus of flowering plants in the family Cannabaceae that is widely accepted as being indigenous to and originating from the continent of Asia. However, the number of species is disputed, with as many as three species be ...
deemed for personal use. Subsequent figures obtained from NSW Police in 2023 revealed that between 1 January 2013 and 30 June 2023, officers had conducted 94,535 personal searches (refers to both strip searches and less invasive frisk or "general" searches) resulting from drug detection dog indications, with only 25% resulting in illicit drugs being found. In late 2014, reports were first published alleging that NSW Police were routinely using drug detection dog indications as a justification for conducting invasive strip searches, particularly at major events such as music festivals (see New South Wales Police Force strip search scandal). Data obtained from NSW Police shows that between 1 July 2014 and 30 June 2020, officers conducted 27,835 strip searches "in the field" (outside of a police station).Inquiry into NSW Police Force strip search practices.
Law Enforcement Conduct Commission. December 2020
Separate data shows that during the same six-year period, officers conducted 5659 strip searches resulting from drug detection dog indications. In October 2018, the Law Enforcement Conduct Commission launched a formal investigation into the use of strip searches by NSW Police. In a final report handed down in December 2020, the commission found that there had been a "significant increase" in the "number and proportion" of strip searches carried out following drug detection dog indications in the five years between 2014 and 2019. In July 2022, a
class action A class action is a form of lawsuit. Class Action may also refer to: * ''Class Action'' (film), 1991, starring Gene Hackman and Mary Elizabeth Mastrantonio * Class Action (band), a garage house band * "Class Action" (''Teenage Robot''), a 2002 e ...
was filed in the
Supreme Court of New South Wales The Supreme Court of New South Wales is the highest state court of the Australian States and territories of Australia, State of New South Wales. It has unlimited jurisdiction within the state in civil law (common law), civil matters, and hears ...
on behalf of patrons strip searched at music festivals by NSW Police from July 2016 onwards. Head plaintiff for the class action is a then 27-year-old woman who was wrongly strip searched at the Splendour in the Grass music festival in 2018 after being stopped by a drug detection dog.


United States

The 1983 Supreme Court decision '' United States v. Place'' ruled that it did not violate a person's Fourth Amendment rights to have a dog sniff a person's luggage or property in a public place without a search warrant or
probable cause In United States criminal law, probable cause is the legal standard by which police authorities have reason to obtain a warrant for the arrest of a suspected criminal and for a court's issuing of a search warrant. One definition of the standar ...
. This was extended to include routine traffic stops in '' Illinois v. Caballes'' (2005), provided it does not unreasonably prolong the duration of the stop. In his dissent, Justice
David Souter David Hackett Souter ( ; September 17, 1939 – May 8, 2025) was an American lawyer and jurist who served as an Associate Justice of the Supreme Court of the United States from 1990 until his retirement in 2009. Appointed by President George H ...
observed:
The infallible dog, however, is a creature of legal fiction. Although the Supreme Court of Illinois did not get into the sniffing averages of drug dogs, their supposed infallibility is belied by judicial opinions describing well-trained animals sniffing and alerting with less than perfect accuracy, whether owing to errors by their handlers, the limitations of the dogs themselves, or even the pervasive contamination of currency by cocaine.
In 2011, civil rights activists claimed that detection dogs responses are influenced by the biases and behaviors of their handlers, which can hinder accuracy. Another factor that affects accuracy is residual odors. Residual odors can linger even after illegal materials have been removed from a particular area, and can lead to false alarms. Additionally, very few states have mandatory training, testing, or certification standards for detection dogs. This leaves people to question whether they are truly equipped to carry out searches. The question of the reliability of drug detection dogs was examined in 2013 in the Supreme Court case '' Florida v. Harris'', which held that courts can presume the accuracy of an alert from a dog that has certification or undergone continuing training. Several ''
amicus brief An amicus curiae (; ) is an individual or organization that is not a party to a legal case, but that is permitted to assist a court by offering information, expertise, or insight that has a bearing on the issues in the case. Whether an ''amic ...
s'' argued that drug dogs show poor accuracy in the field, with up to 80% of alerts being
false positive A false positive is an error in binary classification in which a test result incorrectly indicates the presence of a condition (such as a disease when the disease is not present), while a false negative is the opposite error, where the test resu ...
s. Also in 2013, the Supreme Court ruled in '' Florida v. Jardines'' that having a drug dog sniff the front porch of a private home is considered to be a search within the meaning of the Fourth Amendment, requiring both probable cause and a search warrant. False alerts by dogs have led to wrongful convictions. Sniffer dogs can be trained to detect crop pests and diseases. A study by the US Department of Agriculture found that sniffer dogs identified trees infected with citrus greening disease with 99% accuracy; they could detect infection as early as two weeks after onset.


Civil rights

Detection dogs give police the potential to conduct searches without cause, in a manner that is unregulated. They are often accused of being motivated more by the state's desire to be seen doing something than by any serious desire to respond to the dangers of drugs use. In June 2012, three Nevada Highway Patrol officers filed suit against
Nevada Nevada ( ; ) is a landlocked state in the Western United States. It borders Oregon to the northwest, Idaho to the northeast, California to the west, Arizona to the southeast, and Utah to the east. Nevada is the seventh-most extensive, th ...
's Director of Public Safety, alleging that he violated the police dog program by intentionally training canines to be "trick ponies" to falsely alert based on cues from their handlers ( Clever Hans effect) so as to enable officers to conduct illegal searches of vehicles. The lawsuit claims that in doing so, he and other top Highway Patrol officers had violated the federal
Racketeer Influenced and Corrupt Organizations Act The Racketeer Influenced and Corrupt Organizations (RICO) Act is a United States federal law that provides for extended criminal penalties and a civil cause of action for acts performed as part of an ongoing criminal organization. RICO was e ...
(RICO Act). In Norway, students were subjected to a drug search in their classroom by a detection dog. The students didn't have to be present in the room while the dogs searched; however, they were forced to answer questions by the police instead. An article in ''Tidsskrift for strafferett'', Norway's journal of
criminal law Criminal law is the body of law that relates to crime. It proscribes conduct perceived as threatening, harmful, or otherwise endangering to the property, health, safety, and Well-being, welfare of people inclusive of one's self. Most criminal l ...
, claims that such searches breach Norwegian law. Detector dogs have been used by secret police and security services to support campaigns of political persecution. For example, sweat collected from subjects following interrogation was used by the
Stasi The Ministry for State Security (, ; abbreviated MfS), commonly known as the (, an abbreviation of ), was the Intelligence agency, state security service and secret police of East Germany from 1950 to 1990. It was one of the most repressive pol ...
to train dogs to respond to their scent.


See also


References


Further reading


NPR's ''All Things Considered: Using Dogs to Sniff Out Bed Bugs''

Fox Philadelphia: "Bed Bug Dog and Bed Bug Control Experts discussing use of Bed Bug Dogs"
*Braverman, Irus. 2013.
Passing the Sniff Test: Police Dogs as Surveillance Technology
" ''Buffalo Law Review'' 61 (81): 81–167. *Blum, Binyamin. 2017.
The Hounds of Empire: Forensic Dog Tracking in Britain and Its Colonies, 1888-1953
" ''Law and History Review'' 35: 621–65.


External links

{{Working animals Dog training Explosive detection Scent hounds Working dogs Police dogs