Rear Seat Expansion Kit with Helmet Kits or Headsets is designed to expand your two-person intercom system to 4 persons. Options are available in headset and helmet kit for both STX Stereo and Mono Intercoms with 16' cables for back seat connectivity. AlphaBass headset features include TRUE Carbon fiber, leather ear seals, Flex Boom Mic, M101 Red dynamic noise cancelling mic, and easy volume and bass control. Ultimate Mono and STX Headset come with Carbon Fiber style finish, Flex boom mic, M101 red dynamic noise cancelling mic, hard wired cabling, large comfortable gel ear seals, cloth ear covers, and easy volume control. Mono and STX Helmet Kit offer Alpha Audio speakers, Clear Hear speakers, Dynamic Noise Canceling mic, and easy to install Helmet speakers with peal and stick adhesive. Package includes two headsets or helmet kits and two 16' intercom cables. Compatible with various STX and MONO intercoms.