What is a knocklink and what does it do? Roughly how much do they cost and should I get one?

Thanks guys.

 

Knocklink measures engine knock (or detonation) using a microphone, and displays it as several LED's, going from mild to very bad sh@t!! They cost about £150 with a sensor and if you modify your car, or if it is an import, they are IMHO essential for peace of mind. Remember your car may be fine in normal conditions but when running on a hot day (say on track) or with bad fuel, £150 may save a rebuild! If the lights come on, its time to back off!