For sale: Link G4 KnockLink Kit (Knock Sensor Interface + Sensor + Loom G4KNLK). Used very lightly and in excellent condition. The device's function: It is a smart alarm system to protect the car engine. The sensor reads and checks for knocks or detonation inside the engine and gives the driver an immediate red visual alert to avoid engine damage or piston breakage during hard acceleration. Its advantage is that it is a completely independent external system (can be installed on any car) and is very easy to install.