Abstract: A locking mechanism for locking and/or unlocking a door, window or the like comprises a barrel having a number of apertures, each aperture being connected to a light emitter or a light sensor via an optic fibre. A key for insertion into the barrel is also provided with a number of apertures internally connected via optic fibres for optically connecting selected ones of the apertures in the barrel together. When the key is in place, continuous light paths are provided between the light emitters and the light sensors, the latter being arranged to actuate the locking mechanism.