4: Plug in your BT TwinTalks
Then plug your second BT TwinTalk into your other extension socket. Look at the Ring LED on each unit. If one of the Ring LED indicators is permanently lit, then it means you have a reversal in the polarity of your wiring to your extension socket.
This can be very easily solved by following these instructions.
You can test other extension sockets to which you want to connect BT TwinTalks in the same way.