I have a music channel on in the background on the TV. My phone is listening in and identifying the songs. I don't like the idea of phones sending audio data to Google, but I read that the identification is done on the phone itself. I was sceptical... When you think about it, how much data would it have to store to be able to identify potentially tens of thousands of songs? (It has named all the songs so far this evening, including many that I have never heard before.) I just turned off phone data and wifi and... yes, it can still identify the songs!
It must be doing some serious number crunching to derive some kind of compact digital fingerprint for each song and store that for comparison.
At first, I suspected that it might be transcribing lyrics and identifying them. Nope - it identified several songs before the singer uttered a word!
I'm going to see if I can find any information about this function. I find it fascinating. (More interesting than the music, actually!)