Sixty years ago this month, the September 1960 issue of Popular Electronics showed how to put together this one-way carrier current intercom. It could be used to listen to the nursery, garage, or other room, anywhere in the house. The transmitter was a simple one-transistor oscillator, using a speaker as the microphone. It sent the signal through the house wiring to another room, where a pickup coil was plugged in and placed near a radio set to a clear spot at the bottom of the dial. Despite the low power, this hookup allowed the signal to be monitored anywhere in the house.

According to the magazine, the parts cost was about $10.