Replacement transmitter for the FieldTrainer® 425 and 425S. The SD-425 system is fully customizable, allowing you the flexibility to set 2 or more transmitters to control the same collar receiver. Consult your Owner's Manual for set up instructions. More Info Compatible with: FieldTrainer® 425 (SD-425), 425S (SD-425S) WetlandHunter® 425 (SD-425CAMO), 1825 (SD-1825CAMO) SportHunter® 825 (SD-825), 1225 (SD-1225), 1825 (SD-1825) ProHunter® 2525 (SD-2525) HoundHunter® 3225 (SD-3225)