Plug into a spare phone extension socket, when the phone rings that is plugged into a different phone socket the box acts as a ring amplifier. There is white paint on the sides of the casing caused when the wall was painted around it.
BT Loud Indoor Telephone Extension Bell 50E British Telecom Unused Tatty Box
BT Loud Indoor Telephone Ringer Amplifier extension tonecaller & fixings
BT Loud Indoor Telephone Bell British Telecom Bell 50E - New/Sealed
BT Loud Indoor Telephone Bell British Telecom Bell 50E
BT Loud Indoor Telephone Ringer Amplifier extension tonecaller aid hearing loss
