I've been poking this the last few hours. It uses both audible and inaudible (ultrasonic) frequencies. The URL is passed to a Google service called Copresence to transform it into a short token - it's this token that's played. The Copresence client, and the playing/listening code are part of Chromium/Chrome 43.x. I think earlier versions won't work with the extension.<p>Google Tone is similar to <a href="http://chirp.io/" rel="nofollow">http://chirp.io/</a>, which has iOS and Android apps. There are third-party transmitters (but not listeners) which work across browsers. <a href="http://piupiu.ga/" rel="nofollow">http://piupiu.ga/</a> is the most complete. I wrote a bookmarklet <a href="https://moreati.github.io/chirpweb/" rel="nofollow">https://moreati.github.io/chirpweb/</a>.
Note that this technique has a pretty neat malicious use case: bridging air gaps, in a way that removing/disabling wireless chips won't stop. You'd have to have already installed malware to the airgapped machine, of course, but once that's done, chances are it'll frequently be in range of (presumably easier to compromise) Internet-connected machines, and ultrasound allows slow but bidirectional communication.<p>This was alleged in 2013 to have been done in a piece of malware dubbed "badBIOS", but said malware is likely imaginary.<p><a href="http://arstechnica.com/security/2013/10/meet-badbios-the-mysterious-mac-and-pc-malware-that-jumps-airgaps/" rel="nofollow">http://arstechnica.com/security/2013/10/meet-badbios-the-mys...</a>
Oh hey, I actually built something extremely similar in a hacknight recently [1]. Except instead of just converting URLs to fixed size tokens (also how chirp.io works), I allowed arbitrary bit streams and forward error correction.<p>[1] <a href="https://github.com/rraval/pied-piper" rel="nofollow">https://github.com/rraval/pied-piper</a>
I think it's worth mentioning that this is yet another fairly cool project that relies on an always-on* microphone. I don't remember who said it, but there was a very nice quote on HN recently about the currency of freedom i.e. it's not something you should never spend, but you should be certain you're getting your money's worth. :I<p>*I realize you can turn it on and off, but it's not designed to be done easily.
It would be interesting to see something like this with but tweaked to produce sounds like, say, the background bleep bloop perchweeep noises in Star Trek.
would be nice if humans and computers could both produce/consume the audio. That way you would have a secret language that you could perfectly communicate to computers with.