We know what you're listening to

[PopHistorian]

Arbitron is the USA's radio ratings company. They used to send out logs and pay people a few dollars to write down when, where, and to which radio stations they listen to. But, no more. Now they do it electronically, and at the same time reveal that there are inaudible signals going out over the radio.

_http://www.wired.com/techbiz/startups/magazine/15-09/st_arbitron

Arbitron Portable People Meter Eavesdrops on Your Musical Life

... Since the 1960s, the survey-research company has paid listeners to keep a handwritten log of every station they tune in to. Arbitron crunches the numbers, releases the ratings ...

Now, with the introduction of its Portable People Meter ... gadget clips to listeners' clothing, eliminating the log. Participating broadcasts are encoded with an inaudible ID code, which is picked up by a sensor in the device... "Your only job is to carry it," says Arbitron's Thom Mocarsky. "And we know when you do."

was rolled out in New York and Houston this summer. It'll go nationwide by 2010...