Rear Seat Expansion Kit with Helmet Kits or Headsets offers expansion packs for extending a two-person intercom system to 4 persons. Suitable for STX Stereo and Mono Intercoms, it comes with 16' cables for back seats compatibility. The AlphaBass headset features carbon fiber, leather ear seals, Flex Boom Mic, M101 Red dynamic noise cancelling mic, volume and bass control. The Ultimate Mono and STX Headset features a carbon fiber style finish, Flex boom mic, large comfortable gel ear seals, cloth ear covers, and volume control. The Mono and STX Helmet kit features Alpha Audio speakers, Clear Hear speakers, Dynamic Noise Canceling mic, and helmet speakers with sticky adhesive. The kit includes (2) Headsets or Helmet Kits and (2) 16' intercom Cables. Compatible with various STX and Rugged Radios MONO intercom models.