The Leviathan - V2 optical is one of the most advanced ETU (electronic trigger unit) on the market. It combines optical and switch sensors for better handling and durability. Built-in wireless communication for quick setup using iOS or Android smartphones! Tactile trigger switch has travel only 0,13mm long for ultimate hair trigger feeling. Unique Real feel trigger system (RFTS) with integrated spring simulates trigger resistance like in the real gun. It adds secondary resistance with release after the fire. RFTS was designed by professional gunsmith for more realistic feel from shooting. External output and input port serves for custom accessories. Real time response for change settings -> immediately test result. Easy installation into the gearbox (fully integrated inside the gearbox instead of the original trigger contacts) New functions are for free for every user via online update. The Leviathan - V2 optical brings endless possibilities for your gun! Leviathan – V2 optical supports these airsoft guns: 2 YEAR WARRANTY - M4, M16, HK416, AR15 with V2 gearbox according to TM design - M4 with V2 gearbox from Krytac company - SR25 with V2 gearbox according to TM design - ICS SSS gearbox V2 with Cover for the gearbox - MP5 with V2 gearbox according to TM design - G3 with V2 gearbox according to TM design - G&G G2 gearbox V2 (version 2.1 - DIY add empty mag. micro switch to Leviathan input port) - M249 with V2 gearbox according to TM design - M107 BARRETT from Snow wolf company - And others ... Leviathan - V2 optical is not compatible with these gearboxes: - KWA gearbox V2.5 - S&T or Arcturus gearbox V2 - Ares Amoeba gearbox V2 - APS eSilver edge gearbox V2 - Gearbox V2 with microswitch - And others ...