Canary in a Coalmine is a popular idiomatic phrase, used for referring to an early indicator of danger, used similar to the term Redflag.
The expression itself is an allusion to the practice of coal miners, where they took a canary into the mine along with themselves, in order to detect dangerous gases in the shaft.
If the miners noticed that the bird had died, they had a chance to quickly withdraw from the mine, saving their own lives.
“Canary in a Coalmine” didn’t need a lot of time to turn into an allusion, used by the bigger public, to refer to a signal for a threat.
Although the exact origin of the phrase “Canary in a Coalmine” is not known, it was likely created during the industrial revolution, when coal, the lifeblood of industrialization, needed to be extracted on a massive scale.
One of the earliest cases of the expression appearing in print can be found in a copy of the newspaper Yorkshire Telegraph and Star, published on December 21st, 1906.
In the following decade, the occurrence was referenced in newspapers both in Europe, as well as the United States, slowly ingraining in the speech of people across the Anglosphere.
Despite a wide variety of newspaper publications, featuring the phrase, “Canary in a Coalmine” spread moderately in the first half of the 20th century. It was in the 1960s, that the allusion started to become a widely used idiomatic expression.
However, following the 60s, it appeared in publications, novels, poems, as well as movies and cartoons, spreading it further across the population.
Although it is recognized and used both in the US and the UK, it is more widespread in America.
“Canary in a Coalmine” had become a popular expression, indicating a danger that can be perceived early on, and it is still featured today in a wide range of media, including the countless songs, named after the expression.