Signal transmission device of a signaling security system for the secure transmission of signal information of an AC signal to a processing unit, which device has: • an input circuit for detecting the AC signal, the input circuit comprising a first input channel and a second input channel, • an output circuit for evaluating the AC signal, the output circuit comprising at least one first output channel and at least one second output channel, the first output channel and the second output channel being galvanically isolated from one another, the first input channel being connected to the at least one first output channel via a first coupling element, but galvanically isolated from the at least one first output channel, the second input channel being connected to the at least one second output channel via a second coupling element, but galvanically isolated from the at least one second output channel, each input channel (14a, 14b) comprising a plurality of resistors (16a - 16f) connected in series, characterized in that at least two of the resistors (16a - 16f) of each input channel (14a, 14b) differ in at least one characteristic variable, and in that each input channel (14a, 14b) comprises a plurality of voltage direction-dependent electronic switching devices (19a - 19f) connected in series, at least two of the voltage direction-dependent electronic switching devices (19a - 19f) of each input channel (14a, 14b) differing in at least one characteristic variable, the voltage direction-dependent electronic switching devices (19a - 19c) of the first input channel being electrically connected to the AC signal source with opposite polarity to the voltage direction-dependent electronic switching devices (19d - 19f) of the second input channel. • an input circuit for detecting the AC signal, the input circuit comprising a first input channel and a second input channel, • an output circuit for evaluating the AC signal, the output circuit comprising at least one first output channel and at least one second output channel, the first output channel and the second output channel being galvanically isolated from one another, the first input channel being connected to the at least one first output channel via a first coupling element, but galvanically isolated from the at least one first output channel, the second input channel being connected to the at least one second output channel via a second coupling element, but galvanically isolated from the at least one second output channel, each input channel (14a, 14b) comprising a plurality of resistors (16a - 16f) connected in series, characterized in that at least two of the resistors (16a - 16f) of each input channel (14a, 14b) differ in at least one characteristic variable, and in that each input channel (14a, 14b) comprises a plurality of voltage direction-dependent electronic switching devices (19a - 19f) connected in series, at least two of the voltage direction-dependent electronic switching devices (19a - 19f) of each input channel (14a, 14b) differing in at least one characteristic variable, the voltage direction-dependent electronic switching devices (19a - 19c) of the first input channel being electrically connected to the AC signal source with opposite polarity to the voltage direction-dependent electronic switching devices (19d - 19f) of the second input channel. the first input channel being connected to the at least one first output channel via a first coupling element, but galvanically isolated from the at least one first output channel, the second input channel being connected to the at least one second output channel via a second coupling element, but galvanically isolated from the at least one second output channel, each input channel (14a, 14b) comprising a plurality of resistors (16a - 16f) connected in series, characterized in that at least two of the resistors (16a - 16f) of each input channel (14a, 14b) differ in at least one characteristic variable, and in that each input channel (14a, 14b) comprises a plurality of voltage direction-dependent electronic switching devices (19a - 19f) connected in series, at least two of the voltage direction-dependent electronic switching devices (19a - 19f) of each input channel (14a, 14b) differing in at least one characteristic variable, the voltage direction-dependent electronic switching devices (19a - 19c) of the first input channel being electrically connected to the AC signal source with opposite polarity to the voltage direction-dependent electronic switching devices (19d - 19f) of the second input channel.