The H2O Add-On Collar unit can be added to any existing H2O 1800 PLUS series training system (excluding Beeper models) to expand your unit up to a 3-dog system. This Add-On Collar can also replace a lost or damaged collar for all H2O 1800 and 1800 PLUS series systems (excluding Beeper models). Programming to your existing system is fast and simple.Key Features:* Digital Technology* Adds to any H2O 1800 PLUS series training system(excluding Beeper models)* Replaces any lost or damaged H2O 1800 seriestraining system (excluding Beeper models)* Up to 1800 yard (1 mile) range* Lightweight and waterproof* MAXX-Range Internal Antenna System* Rechargeable Ni-MH batteries* Built-in safety shut off system* Available Limited Lifetime WarrantyPackage Contents:* 1 x Collar Unit w/ Green collar belt* Double-jack Cable