This bundle contains the FieldTrainer 425X e-collar system with an additional collar allowing you to train two dogs with one remote. Be sure to reference the operating guide to adjust your remote to a multi dog mode before starting training. The SD-425X is our smallest and lightest e-collar built for in-the-field training or hunting with close working dogs. Consistency and perfect timing are critical to developing your sporting dogs, so the remote is quickly and easily operated without having to look at it - which lets you focus on your dogs and not your equipment. With only a slight movement of the dial and the push of a button, you will be able to deliver a tone or vibration, and static stimulation. Use these stimulation types to communicate with your dogs out to 500 yards with any of the 425 models.