knock sensor/gauge

Yeah, there are different kinds of sensors. The most basic are essentially just microphones (piezoelectric elements for the engineers out there). They produce a voltage when they are vibrated, so you can more or less just attach them to headphones or a scope. The amount of voltage they produce is based on the severity of vibration, so they'll have lots of electrical "noise" all the time and then spike under conditions like knock (or hitting a hammer on the engine block as a way to test them). I believe Dodge uses the tuned variety mentioned above. I think they operate in a similar fashion (produce a voltage based on vibration strength), but I believe they filter out a lot of the "noise" and only really respond on larger signals. Typically I'm fairly sure they are engine specific though, so they are sensitive at whatever frequency the engineers determined the engine knocks at. This would mean you couldn't necessarily just go out and buy a sensor and expect it to work.

The more simple "microphone" type are usually just a single wire hookup and I believe are farily common to GM. I know the sensors on my 5.7 Hemi are a two wire variety, but I still haven't figured out how to test them.