DT Systems H2O - Add On CollarMake your H2O 1810PLUS, 1820PLUS, or 1830PLUS a multi dog system Add on or Replacement Collar Receiver for the H2O 1810PLUS, 1820PLUS, or 1830PLUS. Available with your choice of Black, Orange, or Green collar straps. Black is recommended if you need to replace the original collar receiver that came with your H2O system. Orange and or Green are recommended to expand your H2O PLUS unit to a 2 dog or 3 dog system. Features: Lightweight Waterproof 16