Hi PETE, OK HERE GOES :IF YOU HAVE AN EXISTING BELL/TRANSFORMER RUN FROM CU ITS A TWO MINUTE OF PUTTING IN A SUPPLIED CABLE IN THE EXISTING BELL AND WIRE UP BELL AT THE DOOR JOBS A GOOD UN. THE PRO RUNS AT 24V AC AND PRETTY MUCH ALL UK BELL TRANSFOMRERS RUN 12V AND THATS NOT ENOUGH SO SUPPLIED CABLE HELPS YOU USE EXISTING BELL BUT THE SUPPLIED DIN RAIL TRANSFORMER MUST BE CHANGED AT THE CU . I HAVE NEITHER EXISTING BELL OR TRANSFORMER AT THE CU , SO THE QUICKEST WAY FOR ME AND SAFE WAY IS THE BELL CAN BE RUN FROM A MAINS PLUGGED IN TRANSFORMER . TRANSFORMER TO RING PRO AND READY TO GO ,INCLUDED IS A WIRELESS CHIME AND IS SET UP OVER WIFI WITH THE BELL . REGARDS LEE