My little brother used to do electrical installations. He once set up a device that deactivated the power in a building as soon as no more consumers were on. Of course that thing is probably still using power continuously itself.
On that same note, shouldn't it be possible to install a mechanism that doesn't use any power at all? Something like, uh, I'm not gonna say a light switch, but a weightless switch, to mix a few metaphors here.
Nanowatts are -60 dBm or what you would expect to receive on your cellphone when you have decent but not great signal. Many radios operate down to the -110 dBm/MHz PSD or lower ranges for high performance stuff. So you could use hits those power levels with energy harvesting on radio waves but only if you were in the right location, on the right band, and it would possibly cause problems for the systems that are trying to use those signals for their intended purposes.
On that same note, shouldn't it be possible to install a mechanism that doesn't use any power at all? Something like, uh, I'm not gonna say a light switch, but a weightless switch, to mix a few metaphors here.