Its a black box about the size of a cigar box that has a rotary selector switch, a jack for headphones and 8 jacks for microphone inputs.

To use the it you temporarily attach the microphones to wherever you think the noise might be coming from and run the wires back to the central black box. You then operate the car with the headphones on and selectively switch the microphones to the headset via the rotary switch. Using the differently placed microphones makes it pretty easy to zero in on the source of a noise. Depending on how well you guess where the noise was coming from you might have to re-position the microphones a couple of times.

The thing is very effective for finding bearing noises on transmissions of differentials since you can place the microphones on different points of the differential or transmission. Its also more effective on noises that constantly occur as opposed to intermittent noise since you have to be able to rapidly switch between the microphones to compare the noise signatures.

I'm not sure how much it costs, I received mine as a gift but I would think you could build one for about $50 in parts. There is nothing 'high tech' about it.

Tim