#if your canary starts beeping calmly evacuate the building

[21st-century-minutiae]

Mines run the risk of accumulation of toxic gasses or poor air circulation that can lead to incapacitation or death for miners. These gasses might be invisible or indistinguishable from the debris created by mining. Historically, before the advent of air quality detectors and the like, minors would bring a songbird like a canary down with them. Being much smaller than a human, a canary would die when exposed to toxic gasses much more quickly than a human would, If the bird died, miners would have ample time to retreat to safety.

In the early twenty-first century, this practice is no longer required, as we have much better technology for air quality detection and circulation. However, it survives in the english language as an idiomatic expression. A "canary in a coal mine" is an indicator that detects when things go wrong while you still have time to escape. It can be used in the future tense (e.g. "the price of bread will be our canary in the coal mine), to indicate that it is something people plan to keep a close eye on in case there is a danger. It can also be used in the past tense (e.g. "the temperature of the water was the canary in the coal mine"), to indicate that people SHOULD HAVE paid attention to a sign that was obvious in retrospect, or that they successfully noticed a sign. Generally there is an implication that the metaphorical canary is NOT the cause of the disaster it foretells, but an early consequence of such.

im the prettiest canary in this mine