Sniffer Dogs – Canine Snitches

This entry is part 5 of 8 in the series UK Police


A detection or ‘sniffer’ dog is trained to use its nose to detect various substances (or traces of their recent presence) in a given environment. Police and other law enforcement agencies utilize various species (e.g. Beagle, Belgian Malinois, Bloodhound, Cocker Spaniel, German Shepherd, Labrador Retriever, and Springer Spaniel), trained to detect currency, explosives, drugs, human remains, tracking, mobile phones (useful in prisons), invasive species of flora and fauna, fire accelerants, firearms, CDs/DVDs, and other evidence.

UK police forces employ over 2500 dogs, though it is not clear exactly what percentage of these specialize in detection work. All British police dogs (and presumably customs dogs too?) must be licensed to work operationally, and are required to pass a test at the completion of their initial training, with more annually until they retire. The average retirement age of such dogs (of whichever discipline) is at 8 years old, with the majority sourced from within specialized breeding programs, intended to produce healthy dogs with strong working ethics. Britain’s largest police dog breeding program is that of the Metropolitan Police, who not only supply London, but also other parts of the UK and other countries.

Despite the success of the Met’s program, the South Korean Customs Service may have gone one better – a 2009 article in High Times magazine reported;

Six genetic duplicates of a single Labrador Retriever have been working at the country’s main Inchon International airport and three other customs checkpoints.”

This information was attributed to a statement from the South Korean government, who apparently hoped that using cloning would reduce the cost of training such dogs.

A potted history of detection dogs

Israel is generally agreed to have been the first country to use drug detection dogs, with the French following suit in 1965, followed by the American military police in Vietnam (in an attempt to stop personnel smuggling drugs back to the U.S.). In 1970, the U.S. Customs Service began to use dogs for the same purpose, with the D.E.A. and state and local police forces starting to do so soon after. Since then many other countries around the globe have adopted the use of detection dogs.

The use of dogs for olfactory surveillance has been criticized as allowing the police to conduct searches without due cause, and in an unregulated manner. It has also been described as ‘show-policing’; “motivated more by the state’s desire to be seen to be doing something than any serious attempt to respond to the dangers of drug use”. An example of this might be that from 2008-2011 in Norway; “probably more than 1000 pupils in about 90 classrooms” suffered a detection drug dog coming into their classrooms, where it was; “voluntary for pupils to be present with the drug dog, but those who want[ed] to leave the classroom must answer some questions to police”. The Norwegian journal of criminal law, Tidsskrift for strafferett, argued that these searches were in breach of law.


The accuracy of police dog indications has repeatedly been called into question around the world. A 2006 report from Australia’s New South Wales Ombudsman stated that illegal drugs were found in only 26% of the state’s police searches resulting from sniffer dog indications, and of these 84% were for ‘personal use’ amounts of cannabis. Furthermore, the report also found such searches to be ineffective at catching drug dealers, with only 0.19% of indications ultimately leading to a successful prosecution.

In 2011, the Chicago Tribune newspaper reviewed the traffic stop data from Chicago-area police departments, finding that ‘false alerts’ were strongly biased against Hispanic suspects, with just 8% of positive alerts on these resulting in the discovery of drugs or paraphernalia (compared to an average of 47% of all positives across all races in the same area and period). While it is likely that some of these ‘Hispanic’ alerts may have been down to residual odours, it is still demonstrable fact that dog responses can be influenced by the biases and behaviours of their handlers.

Later in 2011, researchers at America’s UC Davis University put police detection dogs to the test, resulting in over 200 false alerts (which in the real world would be used to justify searches on people and/or property). The study found that false alerts were more likely when a dog’s handler believed that there was scent present. The handlers were informed that there might be up to three target scents in any one of four rooms, and that these scents were marked by a piece of red paper in the room. However, none of the rooms actually contained any of the relevant scents, yet the dogs still alerted in all, likely influenced by their master’s non-verbal cues stemming from a belief that there were indeed scents present. Subsequently, in June 2012, three Nevada police officers filed suit against the state’s Director of Public Safety, alleging that he intentionally trained police dogs to falsely alert based on cues from their handlers, to enable illegal searches of vehicles.

What to do if a police dog handler stops you

Police use sniffer dogs in public locations where they suspect that they will find people carrying illegal substances, including train and tube stations (e.g. Euston, Finsbury Park, Kings Cross, Liverpool Street, and Willesden Junction), clubs, raves, and festivals. They are not 100% reliable, and may alert their handler that somebody is carrying drugs when they are not, or else might fail to identify someone who does have drugs. Remember that they may also be influenced to alert by their handler, for a variety of (hopefully obvious) reasons.

The UK does not currently have any laws or regulations on the police use of sniffer dogs, only ‘guidance for use’ – this guidance states that the dogs must walk through a crowd and then indicate people, rather than police officers ordering people to walk past the dogs. In reality the dogs are used daily across the UK, as people are funneled past sniffer dogs as they come off escalators at rail stations (a practice believed by Release to be unlawful, yet still unchallenged in a UK court), in clear breach of the impractical and unenforceable guidance.

The police do not have a general power to require you to submit to a dog search, although their standard practice is to treat dog indications as reasonable grounds. If the police try to use an attempt to avoid a dog as grounds for a search, do not resist, as you will risk both physical injury and serious criminal charges if you do. If you believe the search, or any other action by the officer(s), to be unlawful, take action afterwards via the legal system – request a copy of the search record (stating the reason for the stop) and seek legal advice.

If a police dog indicates that you are carrying contraband (or its handler says as much) when you are not, you will likely be asked to provide reasons as to why the dog has picked you out. However, as with many dealings between a member of the public and a police officer, you would be wise to politely refuse to comply, as a record will be made of everything you say, and may count towards the grounds for searching you, or investigating others. If no drugs are found on you, you should be free to leave – ensure that you note down the badge numbers of the officers involved, as these will be required in order to follow up any complaints that you might have. If you are searched and drugs are found on you: do not panic, be polite, say as little as you can, and seek independent legal advice immediately. You can also get legal advice on bringing a civil action against the police after a search has taken place.

Now for the science bit

Dogs smell as we see. Whereas we can see the different types of vegetables in a stew, yet smell only their composite aroma, a dog can smell the vegetables separately. This means that, try as one might to mask the fragrance of a particular substance, the dog will nearly always be able to smell components a, b, c, plus substance. Eventually, all containers of said substance produce a ‘scent cone’ that rises from its source, for which it takes time, heat, motion, and vibration to develop. A detection dog can then sniff the cone out.

Now from time to time the concerned citizen might require the transportation of a substance, one that they wish to avoid being detected by the authorities…with this in mind, a few tips follow – for your education only! The key here is to keep (as near as practical) a sterile packaging environment. As time is a factor in the development of a scent cone, it is best to prepare your package as close to transport as possible.

  1. Use Cellophane wrap (apparently minimally porous) or a ‘food-grade’ vacuum packager to seal your specialist substance. A vacuum by definition prevents airflow, but the Cellophane might suffice in a pinch. Wear gloves when handling your substance – do not touch the outside of the resulting package until wearing a fresh set.
  2. Clean the outside of the package with bleach, to remove any remaining substance residue. Ensure this does not encounter anything else containing the residue, so no smoking, etc. Wear a fresh set of gloves when handling your package – do not touch it until you have put them on.
  3. Rinse the package thoroughly with tap water – detection dogs are often trained to alert on unusual/unexpected smells, hence it would seem prudent to at least attempt to minimise the aroma of bleach.
  4. Place your package into an airtight container, made of metal or dense plastic (Tupperware). Plastic is slightly porous, thus will release odour over time. Temperature has a direct bearing on how much scent is released too. Wear a fresh set of gloves when handling your container – do not touch it until you have put them on.
  5. Clean the outside of the container with bleach. Ensure it does not encounter anything else containing the residue.
  6. Rinse the container thoroughly with tap water to minimise the smell of bleach.
  7. When transporting the resulting package, always attempt to counteract the scent cone’s accelerating factors – minimise heat, motion, and vibration – keep it as cool and as still as possible. Do not forget to conceal it from prying humans as best you can too.


  • No smoking of illegal substances (or any other illegal materials present) around the container at any point – keep it clean!
  • Conjecture regarding the porosity of vacuum packaging – “A single vacuum seal on some MDMA/weed will be able to be detected by a dog within 15 minutes of making the seal. Double vac is like 2-4 days and triple vac is anywhere from 12-14 days to a month or so at max.” (Quoted from the an internet forum, unverified by this author)
  • Detection dogs can apparently only work to a maximum height of 1.2 metres or so (unverified by this author). If this is the case, then, while the scent is heavier than air and consequently will fall, higher positioning of a container would still seem likely to reduce the chance of exposure.

Unanswered questions

  • Are dogs trained to smell traces of precursor-type chemicals? With particular relevance to making it easier to discover harder to detect substances such as LSD (active in such miniscule amounts that a dog exposed to it would likely be tripping balls, although there are non-active artificial LSD scents available for training purposes).
  • Can a dog detect analogues of a drug? For example, if trained to sniff out ketamine, will it also be able to do so for MXE? If so, how different do substances need to be in order for a dog to require specific training? Could one trained to detect ketamine smell all the other members of the arylcyclohexylamine group, or only those most similar in structure?
  • If a dog were trained to sniff out MDMA, would it alert for weed previously stored alongside it? How long would this additional scent be detectable if so?
  • How long do ‘everyday’ residual scents last? If you smoke a spliff on Monday, will it still be detectable by a police dog on Wednesday? Is there a reliable rule of thumb for this?
  • Are dogs trained to alert for the polymers of the plastic baggies (‘dodgy bags’) used by many drug users? As stated on several internet forums, but unverified by this author.
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