In this scenario, the intake charge can be pre- ignited, or ignited in another area of the combustion chamber leading to two flame kernels, abnormally fast burning, and you guessed it, detonation. Fortunately for us, the most common cause of detonation in street Mustang's comes simply from too much timing advance. In this case the flame is ignited by the spark plug. Normally as the flame kernel expands, cylinder pressure climbs, but before it reaches the critical point, the piston is already on its way down, thus averting disaster. In the case where timing is too far advanced, pressure starts building too early and because the piston is still coming up, pressure builds quickly, reaching auto-ignition.
Detonation occurs and cylinder pressure again goes through the roof.
Now that we have a working knowledge of detonation and what causes it, let's take a detailed look at the Safeguard. Like many OEM applications, the Safeguard utilizes a knock sensor. This device is essentially a high quality microphone that screws into the engine's block. The knock sensor is tuned to respond most strongly to those frequencies that are known to accompany detonation. It accomplishes this very quickly, before the troubled cylinder can fire again.