Knock sensor

[Dave Williams]

-> Just interested in other's ideas how this might actually work.  How
-> could plug gap resistance after the spark tell you anything about
-> detonation?

 As chamber pressure goes up it becomes harder for a spark to jump the
gap.  SAAB might be doing that... but you'd actually have to send a
spark, which wouldn't be a good idea before the intended ignition event.
They're probably watching for ionization from detonation combustion.
The resistance across the gap will change if the mixture is burning.