The invention relates to a safety detection system comprising a detection chain formed by a number of interconnected safety detectors (D1, . . . D5). The detectors (D1, . . . D5) in the chain are also interconnected in order to form a diagnostic line in parallel with the safety chain. The first detector thus comprises means for generating diagnostic information comprising its surveillance state, and means for sending this diagnostic information, on the diagnostic line, to the second detector in the chain, which in turn enriches the diagnostic information. At the end of the chain, the last detector is connected to a diagnostic module (MD) intended to receive the diagnostic information, to interpret it, and to control the start-up of the application to be secured.