The idea of capturing stray airwaves is a good one, even if it
is only a marketing ploy.
No. It is snake oil, and no retarded marketing ploy is good. What do
you think is partly to blame for the erosion of this country's economy?
Do the math. RF "Airwaves" equals femtowatts, at best, perhaps a bit
more near the transmitter. So it would take a LONG time or a LOT of
signals (multiple tuners?) to even equal the energy needed to pump the
battery charge circuit in the unit.
Do the math EM energy falls off at a rate of the square of the distance.
That is how flux density degrades through space. Each flux line is the
square of the distance away from the previous set. So too goes the
power.
So putting the coil right next to an "source coil", as is the case with
say, the electric toothbrushes that have no charging pins in the charging
stand does work.
Putting the coil several feet away, makes for very little useable
energy. Even less with unstructured sources like the house wiring
suggestion, less still with rf feeds.
So to the trained person, the idea sucks because it misleads the
obvious lay persons, like yourself, it seems.