The line coupler acts as a message filter on the 2 BUSes connected to it, allowing only those desired to pass. It also electrically separates the 2 BUSes, so each one requires its own 01801 power supply. In the event that the SAI burglar alarm is present, the control unit must be strictly connected to the BUS of the SAI burglar alarm, which is connected to the BUS 1 terminal of the line coupler. The BUS for home automation devices (shutters, relays, etc.) are connected to the BUS 2 terminal.