Knock sensor.

[Rodney_L_Wiggins at keybank.com]

   It seems this discussion has illustrated two separate camps on the Knock
sensor issue: the "simple microphone camp" and the "far more complicated camp".
No offense intended for either group. For those in the  "simple microphone"
camp,  MSD makes a universal knock sensor with an LED bar graph and alarm.
Summit Racing sells it for about $150. It has adjustment for sensitivity and
volume.  It comes with a threaded "microphone" and an adapter to fit different
size holes.  I'm not sure of the manufacturer or availability of the microphone
alone. (if someone knows, please tell me, I need to replace mine).  It appears
to be working on my application, but I'm sure its not as good as it could be,
and I certainly wouldn't tune an engine by it. But when there was a problem it
has warned me of it before I could actually hear the detonation.  Perhaps
everyone knows about this device but no one mentioned it due to a consensus that
it is junk. If so, I apologize.
Rod