How would you like to be able to energize any electrical device in your home., from any where in the world. and do it without paying for a telephone call? You can do it and it's perfectly legal. With the Telephone Triggered Switches you can do just that. The device described here is a circuit, which responds to the sound of the telephone Deli There is no need to make any hard wire connections to the telephone line, and it is this feature which permits you to build and use this device without any permission from the Department of Telecommunications.
You can't even be charged any tariff for using it in these days of high energy costs, it would be economical to turn off the air conditioning or the hot water geyser before you leave the house, and turn it on an hour before you arrived home. It could be used to turn on the lighting in the house, at night, before you return home.