Life for an actual canary in a coal mine could be described in three words: "short but meaningful." Early coal mines did not feature ventilation systems, so legend has it that miners would bring a caged canary into new coal seams. Canaries are especially sensitive to methane and carbon monoxide, which made them ideal for detecting any dangerous gas build-ups. As long as the bird kept singing, the miners knew their air supply was safe. A dead canary signaled an immediate evacuation.
Even as gas detection technology improved, some mining companies still relied on the canary method well into the 20th century. Other animals were used occasionally, but only the canary had the ability to detect small concentrations of gas and react instinctively.
Today, the practice of using a bird to test the air supply has become part of coal mining lore, but the ideology behind it has become a popular expression. The phrase "living like a canary in a coal mine" often refers to serving as a warning to others. The actual canary had little control over its fate, but it continued to sing anyway. In one sense, living this way indicates a willingness to experience life's dangers without compromise.
In another sense, many business and political analysts use the phrase to describe a harbinger of the future. A melting glacier in Alaska, for example, may be described as a canary in a coal mine for global warming. One small event in an isolated area may not seem especially noteworthy, but it may offer the first tangible warning of a larger problem developing. In a political sense, a country's delegation abruptly leaving a meeting could be described as a canary in a coal mine for future negotiations.
Some large corporations also use a similar strategy for future growth or reduction. A small company may be used to test the waters for a new product line, for instance. Even if the company only experiences modest profits or losses, the parent corporation can evaluate the feasibility of the product without risking a large investment. By carefully observing any early indicators, industries can avoid major failures down the road or benefit from a jump on the competition.