Rear Seat Expansion Kit with Helmet Kits or Headsets is designed to expand your two-person intercom system to 4 persons. Options for STX Stereo and Mono Intercoms come with 16' cables. AlphaBass headset model showcases TRUE Carbon fiber, Leather ear seals, Flex Boom Mic, M101 Red dynamic noise cancelling mic and easy to use volume and bass control. Ultimate Mono and STX headsets are hard wired with carbon fiber style finish, Flex boom mic and easy to use volume control. The STX Helmet kit features Alpha Audio speakers, Clear Hear speakers, and an easy to install design. Package includes (2) Headsets or Helmet Kits and (2) 16' intercom Cables. Compatible with STX STEREO and MONO intercoms.