What do you think, what kind of device was the canary inside and what did the miners need it for?
This is a kind of indicator of gas contamination of mines, which was used before the invention of electronic devices. Canaries could feel the content of toxic and explosive gases, even with a small amount in the air. Miners followed the behavior of the bird and worked. If the birds began to show concern or fall, the miners quickly climbed to the surface. However, the birds themselves did not necessarily die. With the normalization of the air, they came to their senses, and therefore soon began to use these devices, inside of which was oxygen, which helps to quickly reanimate the canary.
Such susceptibility of birds is associated with a more complex respiratory system. They can breathe at high altitude, where there is little oxygen, but they become more vulnerable to toxic gases, so poisoning occurs much faster than in humans.