The Lone Wolf by Louis Joseph Vance

It was a sound so slight, so very small and still, that only a super-subtle sense of hearing could have discriminated it from the confused multiplicity of almost inaudible, interwoven, interdependent sounds that make up the slumberous quiet of every human habitation, by night.

Lanyard, whose training had taught him how to listen, had learned that the nocturnal hush of each and every house has its singular cadence, its own gentle movement of muted but harmonious sound in which the introduction of an alien sound produces immediate discord, and to which, while at his work, he need attend only subconsciously since the least variation from the norm would give him warning.