The last time you were in an airport, did you feel your heart rate jump at the sight of vigilant German Shepherds sniffing your bags? While your suitcase may have been entirely contraband-free, the idea that smells, often uncontrollable and undetectable to the human nose, can reveal secrets about you is enough to make even a seasoned traveler nervous.
Use of odor detection by law enforcement is on the rise, as defense attorney and surveillance expert Amber Marks writes in the Guardian. For police forces worldwide, smells are being increasingly relied on to detect drugs, weapons, and stolen goods. A smell alone, in the U.K. at least, can even be considered sufficient evidence to convict someone of a crime. Meanwhile, the technology of smell detection is rushing to meet tightened security needs: canine trainers are teaching dogs to sniff out emotions such as guilt and fear, while electronic noses can now be programmed to identify the “odor signature” of different races or ethnic groups.
Most electronic noses consist of a set of sensors, such as metal oxide semiconductors or electricity-conducting polymers, that react to different compounds in unique ways. By matching a specific smell to its corresponding reaction, technicians can “teach” the nose to recognize almost any odor or smell combination. Production and technology continue to evolve with the demand, with more advanced versions mixing biotechnology and microelectronics to catch smells based on their molecular structure.
Dogs, meanwhile, can be trained to use their approximately 220 million mucus-coated olfactory receptors (roughly 40 times as many as humans) to nose out as many as 10 different “target odors” at one time, with remarkable speed.
But given their increasing importance, it’s worth asking: how effective are these odor detectors? Electronic noses can decipher smells with enough accuracy to distinguish between the scents of Coke and Pepsi, and have been found to correctly identify bacteria samples with between 75 and 100 percent accuracy. Still, their range is often limited (i.e., they can’t detect odors from far away) and their accuracy varies based on the compound in question: tests on Chinese vinegars showed as low as 72.1 percent accuracy—hardly high enough to convince a jury beyond a reasonable doubt.
As for man’s best friend, his nose is far from infallible. Marks points out that the Privacy Ombudsman of New South Wales’ inquiry found “that 74 percent of those searched following an indication by a dog were found not to be in possession of illegal drugs.” And olfaction experts have pointed out another problem inherent in canine searches: “‘Dogs want rewards … and so they will give false alerts to get them. Dogs lie.‘”
Meanwhile, other animals have similarly heightened senses of smell — the list includes cockroaches, moths, and bees, none of which have shown much desire to please their masters for a Milkbone — and studies have reportedly been done in the U.S. and the U.K. to see whether any of them can be trained for odor detection. So who knows — maybe next time you’re passing through customs, you’ll have a buzzing hive waiting to sniff out your suitcase.