Abstract: The detecting method described is conceived for use in a bar code decoding system based on digital processing of signals. it functions to process in real time a signal from an A/D converter and determined the portions of this signal which contain a likely bar code and rejecting the portions that surely do not contain a code. Only the former are signaled to a subsequent decoding process. The method steps are essentially the following: determining local maxima and minima of the digitalized analog signal; determining valid transitions; calculating the side of constant brightness zones located between two successive valid transitions; determining likely codes; if appropriate, repositioning the code starting zone; and if appropriate, analyzing detected potential codes for congruence, and signaling the likely codes.