This is ludacris. Where is this currently being applied, if anywhere in the general wild?
Ludicrous: http://dictionary.reference.com/browse/ludicrous
(Sorry, normally I wouldn't point out a spelling mistake, but hopefully this one is amusing as well as informative.)
The Google Tone extension (http://googleresearch.blogspot.com/2015/05/tone-experimental...) uses both ultrasonic sound and an audible DTMF-based codec.
Audio tones are also used for setting up Google OnHub routers; the router emits a tone and the Google On setup app listens for it. (https://support.google.com/onhub/answer/6246481?hl=en)
> The Google On app will automatically find your OnHub. OnHub will then send a setup code directly to your mobile device via an audio tone. For best results, hold your phone right above your OnHub and reduce ambient noise like music.
Neat method of convenient no-setup wireless configuration. Thanks for posting, haven't realized they've started doing this!