If you’ve never come across the phrase, Lacey’s referring to an old practice where miners would carry canaries with them as a primitive form of gas detection when checking out new seams of coal. Having a far lower tolerance than humans, a canary in the presence of odorless, colorless toxic fumes like carbon monoxide would swiftly drop dead in its cage, and the sudden quieting of its song would alert the people nearby so they could evacuate before suffering the same fate.

Here it’s noise rather than silence sounding the alarm, but otherwise the comparison seems apt.