The Portable People Meter is based on scientific research into human hearing processes that Arbitron conducted in the late 1980s and early 1990s, says Ron Kolessar, Arbitron's director of technology. The company has devised a way (called "psycho-acoustic masking") to embed signals into audio programming. Those signals are undetectable to the human ear but can be received by a portable monitoring device.

The system will work for anything with audio, whether it's radio programming, television content or streaming media.

The inaudible "identification code" is embedded into the audio using a standard rack-sized encoder located at the broadcast station or some other origination point. Once encoded into the audio, the identification code remains intact even after the signal is compressed for digital satellite and cable distribution or Internet streaming.

Consumers participating in the Portable People Meter program will wear a pager-sized device, weighing just 2.5 ounces, that detects identification codes and logs the codes and the times they were received.

The only way to foil the portable meter is to press the mute button, because it relies solely on audio signals for monitoring. That means taverns that mute sports contests would defeat the ratings gizmo.

"Anything that comes out of a logs the code and the time received,'' says Kolessar. "That data is then gathered." Data from multiple docking stations in a home are then sent via standard household wiring to the "household hub," a terminal device that aggregates monitoring data and transmits it back to Arbitron via a standard telephone line. The system awards points based on usage.