Abstract: Invention shows an electro-optical key arrangement comprising for a key of the key arrangement comprises: a transmitter (LED1) arranged (G1,G2,G3) to transmit photon radiation at a wave-length range comprising at least one wave length, into a wave guide forming an optical path, a receiver (LED2) arranged to receive, said photon radiation on said at least one wave length, at least partly from said optical path, and to convert said photon radiation into an electric form to be used for an electric signal, and a detector circuit (D1,D2,D3) arranged to detect changes in said photon radiation received for forming a specific electric signal as a key (Q1,Q2,Q3) specific signal.