Besides being a very popular pet, the Beagle is often used as a detection dog due to his EXTREMELY keen sense of smell. As mentioned previously, Beagles are the dog of choice when it comes to contraband food products, insect pests and they are also often used for detecting narcotics. Historically, that sense of smell was employed to track rabbits, foxes and other types of small game; accompanying the Beagle's heightened sense of smell was its very strong drive to track. All of these Beagle characteristics made it a wonderful hunter and then detection dog, but sometimes it makes for a problematic pet.
When Beagles began being used as detection dogs, it became even clearer just how superior their sense of smell really was. They were able to distinguish between a long list of smells; it was even reported that beagles were able to sniff out substances that were camouflaged with other smells and substances that had been washed off days before. Experts claim that the Beagle sense of smell is around ten thousand times more developed than that of a human. In the canine world, the Beagle's sense of smell is superior even to most other breeds of dog; he is bested perhaps only by the Bloodhound. According to scientists, the Beagle's nose is assisted by his large lips and long ears, which both act to stir up and catch scent molecules and direct them towards he nose. The only fault in their sense of smell is that they must be directly in contact with a surface that contacted the scent item to follow the track or distinguish the scent; indeed, they are excellent ground-scenting dogs but they fall a bit short when it comes to air-scenting. In the US, they were replaced by specifically bred coonhounds when hunters needed to track game that left the ground and took to the trees to hide.
His amazing sense of smell coupled with his desire to follow that scent can sometimes cause problems in a Beagle-containing household. Besides being slightly stubborn, it is very difficult to train Beagles because they are so distracted by all the smells that surround them, both fresh and old; they would much rather sniff their way along a trail than learn commands. For the same reason, a Beagle must ALWAYS be kept on a leash when outside of an enclosed location; the temptation to track is just too strong and your Beagle will be off at the first interesting whiff (not to mention the sight of a small animal). Beagles have been known to get lost or hit by cars because everything around them ceases to exist when their nose is to the ground. If you have your dog in the backyard, you must make sure the yard is enclosed or the Beagle will run off; invisible fences don't work well with these dogs because they will think nothing of taking a shock if the reward is being able to follow a small animal or their scent. They take an enormous amount of pleasure in the chase and there aren't many things in existence that will convince a Beagle to forego that pleasure; after all, it's what they've been bred for.