Expansion external unit kit composed of the external unit EX-DSME (Die-cast aluminium faceplate, wide-angle colour camera, single LED for nighttime lighting, 4 mechanical push buttons to set from 1 to 4 call buttons using DIP-switches, indicator LED for: call sent, lockrelease enabled, audio enabled system engaged, adjustment of speaker volume, adjustment of audio balance, power supply from bus line) and the video splitter 1405 for addition of an expansion external unit (Audio/video switching module for 2-wire digital systems, for the connection of additional EX-DSME,power supply from bus line, 2 DIN modules).