You can actually create an intercom or add a switch to an intercom system without disconnecting the cable, the installation will then be the following:

- On the first existing switch: install the mico-module receiver (54515 for DiO 1.0 / ED-LI-08 for DiO 2.0) which will be connected to the switch, to the light and to the power. This changes your first switch into a wireless DIO receiver.

- On the second existing switch (or third, or more): disconnect the power, protect the power wires by immobilising them; and connect the battery-operated micro-module emitter (54700 for DiO 1.0 / ED-SW-00 for DiO 2.0) to the switch.

This changes your switch into a wireless DIO emitter.
To make things easier, you can also simply replace the existing switch or add a DiO wireless switch (54715 or 54725 for DiO 1.0 / ED-SW-01/02/03/04 for DiO 2.0).