The digital centralised signalling device MSA-6 is meant for optical and acoustic signalling of operation of protections, as well as signalling failures and interferences of work of devices operating in the power and industrial objects. Apart from basic functions of signalling, the device is equipped with an events reorder, and the MKA-4 module enables cooperation with the control system of the substation. It also serves as an engineering port for remote (i.e. via modem) communication with the signalling system, monitoring its status, review od recorded data and change of setup.