A safety communication system for providing a safety function, comprising: an evaluation unit to which a number of series-connected subscribers (20, 30, 40) are connected; the evaluation unit comprising a single signal terminal, a ground terminal for a reference potential, means for providing a predetermined signal for the subscribers; the subscribers (20, 30, 40) each comprising a first subscriber signal terminal (21, 31, 41), a second subscriber signal terminal (22, 32, 42), at least one ground terminal (23, 33, 43; 24, 34, 44) for a reference potential, a sensor (26, 36, 46), and an electronic circuit (25, 35, 45); wherein each electronic circuit (25, 35, 45) is adapted to modulate the predetermined signal so as to signal a critical or non-critical system state which is represented by a sensor signal of the respective sensor; wherein the predetermined signal is modulated such that the state of the predetermined signal is altered in a first signal portion of the predetermined signal in at least one position assigned thereto, and that in at least one assigned position of a second signal portion of the predetermined signal, which is represented by a positive voltage level and which has a length depending on the number of series-connected subscribers (20, 30, 40), the positive voltage level is masked out and forwarded in altered form to the subsequent subscriber (30, 40), wherein the masked-out part of the second signal portion is used to provide a supply voltage for the respective subscriber; and wherein the evaluation unit is adapted to receive the modulated predetermined signal at the signal terminal for evaluating the modulated predetermined signal and for controlling a safety function in response to the evaluation result. an evaluation unit to which a number of series-connected subscribers (20, 30, 40) are connected; the evaluation unit comprising a single signal terminal, a ground terminal for a reference potential, means for providing a predetermined signal for the subscribers; the subscribers (20, 30, 40) each comprising a first subscriber signal terminal (21, 31, 41), a second subscriber signal terminal (22, 32, 42), at least one ground terminal (23, 33, 43; 24, 34, 44) for a reference potential, a sensor (26, 36, 46), and an electronic circuit (25, 35, 45); wherein each electronic circuit (25, 35, 45) is adapted to modulate the predetermined signal so as to signal a critical or non-critical system state which is represented by a sensor signal of the respective sensor; wherein the predetermined signal is modulated such that the state of the predetermined signal is altered in a first signal portion of the predetermined signal in at least one position assigned thereto, and that in at least one assigned position of a second signal portion of the predetermined signal, which is represented by a positive voltage level and which has a length depending on the number of series-connected subscribers (20, 30, 40), the positive voltage level is masked out and forwarded in altered form to the subsequent subscriber (30, 40), wherein the masked-out part of the second signal portion is used to provide a supply voltage for the respective subscriber; and wherein the evaluation unit is adapted to receive the modulated predetermined signal at the signal terminal for evaluating the modulated predetermined signal and for controlling a safety function in response to the evaluation result.