Rear Seat Expansion Kit with Helmet Kits or Headsets are designed to expand a two-person intercom system to 4 persons. The packs are available in headset and helmet kit options compatible with STX Stereo and Mono Intercoms and include 16' cables to extend to back seats. Features of AlphaBass Headset are carbon fiber in models, leather ear seals, Flex Boom Mic, M101 Red dynamic noise cancelling mic, volume and bass controls. Ultimate Mono and STX Headset features include carbon fiber style finish, flex boom mic, M101 red dynamic noise cancelling mic, large comfortable gel ear seals, fixed cables, cloth ear covers, easy adjustments to volume. Helmet Kit properties include Alpha Audio speakers, quality sound, Clear Hear speakers, noise cancelling mic, Helmet speakers with adhesive. Contains (2) Headsets or Helmet Kits and (2) 16' intercom Cables. Compatible with numerous Rugged Radios and PCI Trax products.