2 EVOLUTION OF GAS SENSORS
2.1 Canary in a cage
The canary, normally a very songful bird, is more
susceptible than humans to low oxygen, methane gas, or
CO gas. Because of its highly sensitive nature towards
gases, people used them to detect poisonous gases in
mines. They would stop singing and eventually die in the
presence of these gases, signaling the miners to exit the
mine quickly. This was the first kind of gas sensors used
in 1920s.