It listens to hidden codes in the music which is then transmitted weekly to the agency for analysis.
It only detects music that has the codes embedded and nothing else.
Has anyone heard of this type of audience research. Here is a url http://nz.ipsosmediacell.com/Introduction.html that explains how it works. Incidentally they pay for your time. Not sure I want to do this but the idea of how it works is intriguing. Certainly an improvement on the old diaries