Yes, the Ghost Box (and I have one that I made myself) works by flipping through the frequencies at a rapid rate.
Basically the way you create one is by taking a normal radio that has the ability to scan for a signal and then stop. And you remove that barrier which tells it to stop. So what you've created is something that keeps scanning whether it gets a signal or not.
The best ones are able to scan on many frequency bands. AM, FM, and ShortWave (SW1, SW2).
Now, to address the question of their validity. The scientific side of me says that there is no way it can work. No spirit would have the know-how to manipulate frequencies in such a complex manner as to know where the radio is about to scan and then create an frequency modulated signal to produce a word or phrase. No way! I don't know any people who could do that in life or even know what it would take, much less do so after passing.
But, the observed evidence stands clear that there is in fact something to it. The number of instances in which such a device did yield "On Topic" responses is too large to be random. I built one just to find out if there was anything to it, and I went into it very doubtful that anything would come of it. But much to my surprise, on its maiden voyage we did receive some responses which were to direct questions. So now is that possible?
Here is my take on this. I believe it works a bit like a white noise generator. It creates noise which our minds can then use to matrix into a complete word. I also believe that the spirits or entities in the area can use that to help along their communication with us. Not all of us have a direct link to the other side. We can not all communicate and hear what is being spoken to us as clear as day. But as several new friends of mine have told me now, we all have the ability or should I say potential for it.
So I'm thinking that the white noise simply creates that bit of a push or pressure that our brains can use to link onto these communications and matrix the noise into a valid idea. That would explain why everyone in the room hears the same thing.
We somewhat breached on some of this in another thread:
*HERE*
If this theory is true (and here comes the scientific side of me again) it should be verifiable. If you record a spirit box directly (not with a microphone since you don't want to hear the responses of the people in the room). And also record the responses of the people in the room separately. You now have two versions of a session, one with the responses of the people and one with the spirit box's output by itself.
Then after the investigation you combine the audio from the room where the questions are asked but remove the audio where the responses are given. Play that at the same time as the audio from the spirit box directly and lets someone listen to it. See if they come up with the same responses.
My guess is that they will not. That would go towards proof that it is in fact spirit entities interacting with our minds during the investigation to push us towards hearing a response.
I think I'm going to have to figure out a way to tap into the output of the spirit box and feed it into a Voice Recorder on the left channel, and then leave a microphone on the right channel so I can record the two streams and test this theory.