Our one source of energy
Entertainment has always incorporated a feedback loop of communication between creators and audiences, a way to indicate that a connection was made. Think of how curtain calls and applause work with each other, for instance.
Modern Mechanix blog found an early application of technology to this impulse. French radio listeners in 1937 were offered a small switch that they could press when they liked the current program. The switch turned on a small lamp, and the increased current drain would be reported to the station through a deal between the broadcaster and the power company. There is a more modern counterpart in the UK, where the National Grid reports an up to 10 percent surge as electric tea kettles get switched on after major sporting and other television events.