a system for the transmission of a signal having at least two conditions includes a device for emitting signals that has two oscillators whose signal amplitudes are alternately switched according to the two conditions of the binary signal . one of the oscillators generates a first frequency and the other a second frequency . a reception device is provided and has signal detectors which are independently sensitive to the first and second frequencies so that the reception device supplies , at its output , the binary signal or the inverse thereof , which are received over the first and the second frequencies . a process for the transmission of a plurality of signals or messages having at least two conditions includes the steps of emitting signals indicative of the conditions over different transmission channels and emitting signals indicative of one of the conditions of the messages over a common transmission channel . thus , the messages can be reconstructed after reception of one of the transmitted condition signals . a command signal can be produced when all of the transmission channels are simultaneously activated for a predetermined period .