Why is the knock sensor in coolant?

OK, I was wondering why the knock sensor is in a coolant jacket? Maybe someone could explain to me a little about how this sensor works and why it is there?

The knock sensor is a pressure sensitive resistor,it monitors knock by sound waves.When it senses detonation(knocking)it will retard the timing until the detonation stops.Maybe it is in the coolant to keep it cooler than the block.