It allows to connect up to 4 boards (boards of 1 or 2 lines for 4+N system). Each of the decoder outputs is programmed with a 3-digit MDS address. This address identifies each board connected to each output, differentiating it from the rest of the terminals in the installation. When making a call from the Guard Unit, the MDS address corresponding to the marked home is generated, so that only the decoder that has a programmed output with the generated MDS address will establish communication. The boards connected to a decoder have privacy of the audio communications with respect to the rest of the terminals). DIN-10 rail format to facilitate installation inside an electrical equipment box, or they can be screwed directly onto the wall.