From The Book of Popular Science:
For many years electrical engineers have employed switches and other devices requiring small currents of electricity, to put into operation, through the use of relays and solenoids, controlling apparatus at a distance. This is known as “remote control.” The Televox is a method of attaining the same results, using sound waves as an auxiliary means. The control can be effected over any telephone line, and any telephone will serve as a transmitting station, but instead of speaking into the instrument three small whistles are provided for signalling the message. At the other end of the line there is a telephone receiver containing some special features. When it is connected in the usual manner with a transmitting station, the Televox mechanism is automatically put into action by electro-magnetic means. The receiving mechanism of the Televox contains three steel reeds that are tuned to vibrate at definite frequencies corresponding to the notes of the three transmitting whistles. These reeds carry contact points so that when vibrated they will complete electric circuits and thus put in operation certain electro-magnetic devices which may be used for doing such things as opening or closing switches, actuating magnetic solenoids — which, in turn, can be used for a wide range of work.
If one wished to use the Televox he would ask for its number as for any other telephone call. When the connection was made the buzzer of the receiving station would announce the fact. He would then blow the whistle corresponding to the work he wanted done. The reed attuned to his whistle would vibrate, thus putting into action the proper mechanism. The power needed must, of course, be furnished at the receiving end, the Televox simply connecting up the currents to enable it to do its work. Mechanisms are now available for reading meters, reading the temperature of transformers, ascertaining the height of water in reservoirs; and many other uses will undoubtedly be found for this clever invention. The picture of the Televox, with its inventor whistling into a small pitch pipe (thus making any telephone a dispatching end), will be seen above. The grotesque pasteboard figure was added for a special occasion.