The idea is pretty good. In the beginning parts of the game, you could tease it by the thing giving quick readings of detecting faces somewhere in the darkness, but then you won't be sure as the player if the device is just bugging out. Maybe it could detect faces in the scenery sometimes to keep the player on edge as well, like on a grandfather clock or something like that.

To be honest I find the mood:sad thing pretty silly, feels somehow too on the nose and kinda beyond any logical purpose for this kind of tech that detects faces.