According to a report in National Geographic News, the tiny sensor, discovered in mice, is used to pick up chemical warning signals sent by fellow animals in distress.
Many plants and animals emit airborne molecules called alarm pheromones, which alert members of their species to dangers such as predators.
But, how mammals detected these pheromones has been a mystery.
Now a team from the University of Lausanne in Switzerland has said that the answer lies in a microscopic ball of cells in the nose called the Grueneberg ganglion.
The Grueneberg ganglion was first identified in 1973 in various types of mammals, including rodents, cats, apes, and humans.
These mammals probably all have a nose for danger, the study team said, although the discovery has only been made so far in mice.
The new discovery was made during a study of the Grueneberg ganglion in mice using physiological techniques.
"The ganglion is the only (smell) sub-system that's completely functional at birth, so we were thinking it was important for nipple finding for the baby mouse," said study co-author Marie-Christine Broillet.
But after numerous tests for nipple finding and other possible functions, the team found that the ganglion played a role in danger communication.
The researchers then compared how mice with and without their Grueneberg ganglia responded to alarm pheromones.
According to Broillet, the contrast was very striking.
"The normal mouse immediately gets scared and goes to the corner of the box and freezes," she said. But mice without the ganglia carried on as before, seemingly unaware of the danger signals.
Both groups were able to sniff out cookies hidden in their cages, however, suggesting the altered group's sense of smell was otherwise unaffected.
"The chemical sensor's nose-tip location is ideal for early detection of pheromones," said Broillet.
Stuart Firestein, professor of biology at Columbia University, New York, said that the new finding represents two important scientific advances.
"First of all, it extends a growing appreciation that the olfactory system is not a singular system but is really made up of several subsystems," he said.
Second, the study advances the understanding of how body cells and molecules function together within the nervous system.
The newfound mouse alarm detection system introduces "a new and likely powerful model" for such investigations, according to Firestein.