Can e-Noses Replace Sniffer Dogs?

Sniffer Dogs are currently the front line in bio-security at borders. Once, when I entered a US airport, I was approached by a sniffer dog. It indicated to its handler that my luggage concealed meat. I had just thrown away all the snacks I carried onto the airplane, so I was happy to let the handler see that I had nothing left. It left me wondering, would it be possible for electronic noses, or e-noses, to replace sniffer dogs?

Last year there was a lot of excitement about technology. Many machine learning models indicated that they could improve forensic results towards the gold standard of DNA analysis. Fingerprint tests and Ballistic analysis proved to be particularly enhanced by the computer-aided scrutiny. But other technology has, for years, been chasing and failing to catch up with standard practice. This is particularly the case for so-called ‘electronic noses’ or e-noses. In a previous article on drug detection, I touched on the difference between sniffer dogs and e-noses. With last year’s surge of advancement, it’s time to reassess whether e-noses can replace sniffer dogs.

What are we searching for?

Law enforcement requires exceptional noses to find what is hidden. I imagine that everyone knows that sniffer dogs are trained to detect drugs. But these are not the only things they are trained to look for. Border force dogs, such as the one in image 1, are of course trained to smell out drugs, but they also hunt for money, tobacco, food, guns, and sometimes, people (Border Force).

Image 1: A Border Force sniffer dog.
Credit: Public doman

And those are smells they are trained on. A well-trained dog will point out unusual smells that they have not been trained for, such as trafficked animals and animal parts like ivory (WWF, 2014). Australian detection dogs have found electronics and explosives (AFP, 2022). Search and rescue dogs find people trapped under rubble after earthquakes (Berrigan, 2018). And there are the cadaver dogs, trained to locate human remains (Mueller, 2021).

In addition to law enforcement, medical researchers realized that dogs can be trained to sniff out disease (Kramer, 2021).

Why do we rely on dog noses?

A nose detects volatile chemical compounds in the air. These compounds interact with our nasal receptors and cause what we call scent. Humans have always relied on dogs to sniff things out. Dogs were trained to hunt for food. The reason we depend on dog noses is the lack of scent receptors in the human nostrils. Humans have about 5 million receptors in their noses, whereas dog noses run on about 220 million receptors. Not only this, but they can differentiate between nostrils to determine the direction of a smell (Rozenbaum, 2020). Some breeds in particular are prized as sniffer dogs because of their hunting abilities (K9, 2019). These are vital traits in tracking down hidden things that need to be found.

However, there are suggestions that about 75% of the time, the dog alerted the handler to contraband and nothing was uncovered (NGM, 2024).

How are sniffer dogs trained?

Training dogs is not a harmful process. Dogs are trained by a reward system. The initial process is all about play. The trainer takes the dog’s favorite toy, which is unscented, and the dog has fun trying to find it. Then you add the scent of the items that you wish the dog to learn to the toy, and once the dog finds it, they are given a treat. The hiding places are made increasingly difficult, inside something, or buried. So the dog learns to sniff out the illicit substance to receive a reward.

Another method is giving commands, such as sit or stay and rewarding the dog for obeying. If you expose the dog to the scent, at the same time as the signal and the reward, then the dog knows to look for the scent when the signal is given and it will get a reward. The dogs can be trained on more than one scent (3DK9, 2021, April 26).

None of the training is traumatic to the animal.

What is the best breed for a sniffer dog?

Historically, bloodhounds were trained as hunting dogs for their tracking skills, so you could be forgiven for assuming they would make the best sniffer dogs. They are still used by the police in the present age. But they are not the only dogs that work well for searches.

German Shepherd dogs are highly intelligent, and therefore easy to train. English Springer Spaniels turned out to have the best noses for drugs, but Beagles are often found at airports (3DK9, 2021, August 18). Because of their small size, they are less likely to alarm the people they search (ACLAW, 2024). Doberman Pinschers and America Pit Bull Terriers are also good working dogs(3DK9, 2021, August 18).

And of course, some people are afraid of dogs, if a person moves away from the dog, the handler is likely to assume guilt rather than fear (ACLAW, 2024).

How do e-Noses work?

The alternative to sniffer dogs is electronic noses or e-noses. The form of e-nose that most people are familiar with, is the breathalyzer test for alcohol. Researchers have extended the range of the e-noses beyond just alcohol. The volatile scent compounds in the air are directed to a reaction chamber. There, they interact with sensors which send an electronic signal to a computer chip. The chip identifies them and sends a report. Inside the laboratory, these devices give excellent results (Berrigan, 2018).

Image 2: The old-fashioned version of our modern e-noses.
Crdit: Public doman

Technological advances make for increasingly portable devices unlike the old-fashioned one in image 2.

Can we rely on e-Noses?

One of the best things about e-noses, is they do not require breaks in the way that sniffer dogs do, so they can continue the work on search and rescue, even when the dogs are tired. But, as I mentioned above, it is only in the laboratory that the results are stable. In the outside world, it is difficult to isolate the desired volatile compounds from other scents in the air (Berrigan, 2018). Also, they are affected by temperature and humidity changes, which cannot be controlled outside the laboratory (CORDIS, 2022).

So how do e-noses and sniffer dogs compare?

The process of dog training is arduous and expensive. Chips for e-noses are getting less and less expensive. As mentioned above, the e-noses do not need regular breaks, the device can be handed over to a rested searcher. However, each chip is highly sensitive to one volatile compound. A dog can be trained to recognize several different scents and can distinguish between the smell of drugs on a person who has been to a party, and the drugs themselves hidden in the luggage. The most important advantage dogs have over e-noses is their ability to detect compounds in very low concentrations. And of course, the working life of a dog is longer than that of electronic components (CORDIS, 2022).

In conclusion

There are advantages to both types of smell detection. Dog noses are more sensitive to scent than e-noses, but need to rest. An e-nose would be less likely to spook people who have a fear of animals. Instead of an immediate invasive search, a portable e-nose can check if they carry illicit substances. While in other parts of forensic activity, computer recognition is now a vital part of the work, animals are still top dogs in the search for scents. Perhaps, having both options available would create the most effective working practice.

References

3DK9. (2021). How are Drug Sniffing Dogs Trained to Find Narcotics? 3DK9 Defend Detect Discover. April 26. https://www.3dk9detection.com/news/how-are-drug-sniffing-dogs-trained-to-find-narcotics

3DK9. (2021). 15 Dog Breeds that are Successful as K9 Drug Detectors. 3DK9 Defend Detect Discover. August 18. https://www.3dk9detection.com/news/15-dog-breeds-that-are-successful-as-k9-drug-detectors

ACLAW. (2024). Do Sniffer Dogs Actually Work?. Australian Criminal Law Group.  https://aclawgroup.com.au/blog/aclg-news-and-cases/do-drug-sniffer-dogs-actually-work/

AFP. (2022). New AFP Tech Dogs Taking a Bite Out of Crime. Australian Federal Police. https://www.afp.gov.au/news-centre/media-release/new-afp-tech-dogs-taking-bite-out-crime

Berrigan, T. (2018). Electronic Noses Might Replace Search-and-Rescue Dogs. ScienceNewsExplores. https://www.snexplores.org/article/electronic-noses-might-replace-search-and-rescue-dogs

Border Force. National Dogs Programme: Our Detector Dogs. Home Office. https://assets.publishing.service.gov.uk/media/5a7c9cbae5274a30fa38fdff/Detector_Dogs.pdf

CORDIS. (2022). Why Can’t We Replace Sniffer Dogs With Electronic Noses? Phys.Org. December 15. https://phys.org/news/2022-12-sniffer-dogs-electronic-noses.html#:~:text=But%20often%20canines%20outperform%20them,VOCs%20at%20very%20low%20concentrations

K9 Deployment. (2019). Sniffer Dogs — How do they sniff out drugs? K9 Deployment. October 28. https://www.k9deployment.co.uk/2019/10/28/sniffer-dogs-how-do-they-sniff-out-drugs/

Kramer, J. (2021). These Sniffer Dogs are Learning to Smell the Corona Virus. National Geographic. https://www.nationalgeographic.com/animals/article/see-dogs-trained-to-sniff-covid

Mueller, L. (2021). What to Know About Cadaver Dogs. The Spruce Pets. https://www.thesprucepets.com/cadaver-dogs-1113771

NGM. (2024). Sniffer dogs: How accurate are they? Nyman Gibson Miralis. https://ngm.com.au/sniffer-dogs-accuracy/

Rozenbaum, M. (2020). The Science of Sniffs: Dogs Smelling Disease. Understanding Animal Research. June 19. https://www.understandinganimalresearch.org.uk/news/the-science-of-sniffs-disease-smelling-dogs

WWF. (2014). Detection Dogs and Wildlife Crime. World Wildlife Magazine. (Winter) https://www.worldwildlife.org/magazine/issues/winter-2014/articles/detection-dogs-and-wildlife-crime