The H2O 1850 Add-On Collar unit can be added to any existing H2O 1850 PLUS series training system (excluding Beeper models) to expand your unit up to a 2-dog system. This Add-On Collar can also replace a lost or damaged collar for all H2O 1850 and 1850 PLUS series systems. The Beeper/Locator has 3 functions (Locate, Run and Point mode, and Point Only mode) and is audible from up to 450 yards. Programming to your existing system is fast and simple.