The idea is to use the existing PC microphone to listen to whatever
is heard in the background, be it music, your phone going off or the TV
turned down. The PC then identifies it, using fingerprinting, and then
shows you relevant content, whether that's adverts or search results,
or a chat room on the subject.

And, of course, we wouldn’t put it past Google to store that
information away, along with the search terms it keeps that you've
used, and the web pages you have visited, to help it create a
personalised profile that feeds you just the right kind of
adverts/content. And given that it is trying to develop alternative
approaches to TV advertising, it could go the extra step and help send
“content relevant” advertising to your TV as well.