Where does the phrase to Sing like a canary come from?

The phrase "to sing like a canary" refers to someone who reveals secrets or informs on others, particularly in legal contexts. The expression likely originates from the practice of using canaries in coal mines; miners would bring these birds to detect toxic gases. If the canary showed signs of distress or died, it served as a warning, much like an informant who "sings" to alert authorities. The phrase has since evolved to describe anyone who betrays confidences or cooperates with law enforcement.