Abstract: A contact sensor for monitoring breathing of a subject, comprising: a microphone housing defining a first acoustic cavity, a MEMS microphone disposed within the first acoustic cavity; a second acoustic cavity separated from the first acoustic cavity by a cavity wall having a front surface and a rear surface, the second acoustic cavity at least partially defined by the front surface of the cavity wall; an acoustic conduit formed between the first acoustic cavity and the second acoustic cavity through the cavity wall; and a pressure relief vent having a first end terminating at the second acoustic cavity and a second end terminating outside of the second acoustic cavity.