Apparently you don't need to be a rocket scientist to make one of these, a simple trip to Radio Shack and som tweeking and your good to go. I did find a guy who walks you through the entire process. You can follow along and make your own ghost box just in time for Halloween.
I am a very skeptical person when it comes to things like this, and I'm not sure what to think about ghost boxes. It appears to be utterly random when you see one being used, in fact it literally sounds like you have you hand on the tuner of your radio and you're turning the knob back and forth across static and random radio songs and talk. Then suddenly out of the blue you hear a word jump out that seems to answer the question asked of the spirits. Maybe this will help - pretend like we are asking this question, "Is there anybody here that would like to speak to us?" Now think of the beginning of The Ramones song Rock and Roll Radio, and in your mind put a louder "YES" in there somewhere. You got it! That's what it's like.
I know that our brains will always seek out a pattern when presented with randomness - think of making out images in the clouds. I'm not so sure that ghost boxes are any different than this. If we are expecting to hear a certain reply, I think we can make ourselves believe we have heard it when presented with random "noise". Here are some examples that I found on-line of a ghost box in action.
Like I said I think these devices are questionable, but yet they are fun to listen to. Kind of like our Paul McCartney is dead shows we just did. I don't believe for one second that he died in a car crash in 1966, but I get a kick out of looking for clues! If you find this interesting you should try to track down this 3 CD set. It is not to be listened to in the dark that's for sure!