Knock Sensor: Description
WARNING: This page is about a different car, the 2005 Dodge SX, 2005 Dodge SRT-4, and 2005 Dodge Neon. However, it is still accessible from the selected car via links, so may be relevant.
The knock sensor is bolted to the cylinder block. The knock sensor is designed to detect engine vibration that is caused by detonation or pre-ignition.