Abstract: A combination lock of the dial operated tumbler wheel type comprising lock mechanism components including a fence lever and rotatable members to be rotatably positioned responsive to rotation of a dial, the rotatable members including peripherally gated tumbler wheels and a drive cam driven from the dial, and electro-optical light sensing and electrical signalling means for producing sensible indications at a remote monitoring station signifying movement of components of the combination lock mechanism. This means comprises a marking having optically distinctive reflectivity properties on a component of the lock mechanism such as the driving cam and/or a tumbler wheel and/or the fence lever and optical sensor means positioned to receive light from the optically distinctive marking electrical signal signifying movement of the optically distinctive marking.