How does a Portable People Meter operate when it detects motion?

The Portable People Meter (PPM) operates by detecting motion through its internal mechanisms that monitor the user's movement. When the device detects motion, it activates a green light to indicate that it is functioning properly and recording data accurately. This green light turning on serves as a visual confirmation for the user that the PPM is active and engaged in tracking their media consumption in real-time.

This functionality is crucial because the PPM is designed to gather accurate data about what people are listening to, including radio broadcasts and other audio content. If the green light did not indicate activity, it could lead to confusion regarding whether the device was functioning effectively or capturing the necessary data. Other answers imply different reactions of the green light that do not accurately represent the operation of the device.