Link KnockBlock G4+ (KNB) The G4+ KnockBlock is an important tool for engine tuning and helps to detect knocking, lean fuel/air mixtures, and mechanical issues at an early stage. It is used with headphones, earplugs, or noise-cancelling hearing protection and features special filters that allow you to listen for and detect knocks early on. Features: Listen to one or two knock sensors simultaneously Specially designed filter for better signal-to-noise ratio Compatible with headphones, earplugs, or noise-cancelling hearing protection Long-lasting rechargeable lithium battery Robust CNC-machined aluminum housing 3.5 mm headphone jack with flying leads Compatible with all OEM knock sensors Ability to connect directly to a laptop for engine sound recording or frequency analysis via PCLink G4+ Note! Headphones with their own noise cancellation may be unsuitable for use with KnockBlock. What's in the box? G4+ KnockBlock 2 sensor looms (pre-wired) 1 headphone loom (pre-wired) Quickstart guide