Carl Bialik from WSJ writes "A media-measurement company called IMMI is giving panel participants special cellphones that can take reliable sound samples to track consumer behavior. 'Those snippets -- taken every 30 seconds and altered mathematically so any conversation is made unintelligible -- are transmitted continuously to IMMI,' the Wall Street Journal reports. 'Sounds from headphone devices such as iPods can be transmitted to the cellphones with a wireless accessory. IMMI has been building a database of sound signatures, with help from customers testing the company's services as well as with CD content it has licensed.' The idea is to use the sound signatures to test what media consumers are exposed to -- everything from radio music to movie trailers."