The spirit communication device known as the "ghost box" works by sweeping an AM radio band, and using it as a carrier of any spirit voices that wish to communicate.  The audio is direct recorded and then examined for spirit messages found within the audio bits and white noise that is generated by the device.  The result is a noisy recording containing the questions asked by the user of the device, and at times, relevant answers from those on the other side.

For more on the Spirit Communicator, click here.