FieldTrainer SDR-FS Add-A-Dog is an additional collar for the SD-400.

Features Include: The SDR-FS weighs only 2.8 oz. Fully waterproof and submersible Includes 2 collar straps (green and black) Low Battery Light NiMH rechargeable batteries, which allow for longer usage between charges Lifetime Warranty Fits up to a 23" Neck!