The tracking might refer to listening to conversations that takes place near a shut down phone. The technique might be similar to the one used in laser micropho

The tracking might refer to listening to conversations that takes place near a shut down phone. The technique might be similar to the one used in laser microphones (http://en.wikipedia.org/wiki/Laser_microphone http://en.wikipedia.org/wiki/Laser_microphone), but instead of measuring vibrations, to measure the electro magnetic field variance of phone's microphone.