Abstract: A hinge construction having radiative emitter and detector concealed within the body of the hinge's knuckles so as to be in communication with each other when the hinge leaves, and therefore the door, are in a closed position. This communication is permitted through an opening in a notched collar which is juxtaposed between the emitter and detector elements, the notch being aligned with the emitter and detector when the hinge is closed. The opening of the hinge leaves rotates the collar to misalign the collar notch with the emitter and detector elements, thereby causing an electronics circuit module to form a change of state signal which may then be reported to an external monitoring or alarm system. Closing the hinge leaves to realign the notch with the emitter and detector elements will result in the sensing means being reset.