WHEN MY AUNT was 10, some French radio listeners could press an electric switch to express approval of a current radio program. "Holding down a small switch attached to the base of a small lamp placed near the radio, the increased current drain is shown at the local power plant or substation.
Now being used in France, the idea was first tried out by an American power company working with an eastern broadcasting chain." As John Walkenbach notes, "This method is being used worldwide."
Modern Mechanix -- "Listeners Applaud Program"