Any device which modulates the surrounding radio waves has the possibility of causing radio interference, so it will need licensing and type approval. And something which generates wideband crud will never be approved.<p>This thing is not passive. It is receiving, modulating, and re-transmitting broadband signals.<p>The "rusty bolt" form of radio interference is one of the most common that interference investigators have to deal with.
A surprising amount of power can be collected from stray radio waves. You wouldn't be able to power a full computer or even a phone, but you can do cool things like power a radio: <a href="http://en.wikipedia.org/wiki/Foxhole_radio" rel="nofollow">http://en.wikipedia.org/wiki/Foxhole_radio</a><p>However, indoor "solar" power is a more practical idea: <a href="https://developers.google.com/gdata/articles/radish?csw=1" rel="nofollow">https://developers.google.com/gdata/articles/radish?csw=1</a>
FTA: <i>"To send data to a smartphone, for example, one of the new prototypes switches its antenna back and forth between modes that absorb and reflect the signal from a nearby Wi-Fi router. Software installed on the phone allows it to read that signal by observing the changing strength of the signal it detects from that same router as the battery-free device soaks some of it up."</i><p>Sounds just a bit like one indirect way astronomers search for exoplanets: By looking for fluctuations in a star's light caused by a planet's transit 'across' the star. [1]<p>[1] <a href="http://en.wikipedia.org/wiki/Exoplanet#Indirect_methods" rel="nofollow">http://en.wikipedia.org/wiki/Exoplanet#Indirect_methods</a>
Very _Deepness In The Sky_. Even if the battery-less devices don't have that much computing power yet, this still feels like sci-fi technology- the kind of stuff you always thought ought to possible, but just wasn't yet. Pondering: could they come up with less power-hungry communication protocols that could let battery-less devices communicate with each other?