The times have certainly given way to digital but radio waves are re-defining their value. The Tate Ambient Power Module, patented by Joseph Tate of California, converts radio-wave energy (manmade and natural) into energy that can be used by small appliances such as smoke detectors and clock radios.
The device is simple in its design and composition. The Ambient Power Module (APM) is nothing more than an electronic circuit connected to an antenna and grounded to the earth. Tate made this come to life by just loosely wrapped wire around a 3-inch plastic tube with a whip antenna. This module will deliver low voltage up to several milliwatts dependent upon the local radio noise levels and antenna specifications.
Once put together this crafty little unit can generate 36 volts/9 watts of power, equivalent to the output of several Duracell batteries. Apparently, this device in close proximity to large quantities of metal (bridges, ships, etc) winds up the output. The interesting added bonus to this creative module is that it might also be helpful in forecasting earthquakes by watching the rising and falling energy levels.