Instructions
Purchase healthy, active male canaries. They should have smooth plumage and should sing when in their cages. You'll need two canaries per pit.
Gently lower the canaries into the mine with you, and move them carefully when below ground to prevent them from being injured.
Listen carefully to the canary's song during the workday. If the song stops, check the canary immediately.
Watch the canary. If it stops singing, begins to wobble or sway on its perch, or falls off the perch and lies still on the floor of the cage, evacuate the area immediately; the canary is likely reacting to high levels of toxic gases. Take the canary with you; it may revive in fresh air.
How to Use Canaries in Mines
Between 1911 and 1986, canaries were a common sight in coal mines in the United Kingdom. It might seem strange that miners were keeping caged birds down in the pit with them, but the birds weren't companions: they were equipment. Canaries are very sensitive to the presence of gases (carbon monoxide, for example) that can build up during mining, and workers noted that if a canary stopped singing or fell off its perch, it was a warning for them to evacuate the area to protect their own health. Canaries in mines were phased out in the U.K. starting in 1986.