@matt@oslo.town reminds me of a cable radio switch (for the systems that used multiple twisted pairs at 100V), Norway did it slightly differently and sent the signal via the electricity line but it was received on longwave on a normal radio in fact its like a Rediffusion / British Relay switch (which most people involved in NTS likely weren't born when the system was around, or have only seen it on the wall in grandparents house long after the service was ceased)