Training, field trials and hunting - The Field Trainer 425 series is ready to take control in any environment. Both transmitter and receiver are waterproof, and the system boasts an impressive 500 yard range. Rechargeable collar and transmitter. Seven stimulation levels. Can be expanded to run three dogs without losing vibration or tone feature by buying extra collars. SD-425S has the same features but is set at higher levels for extremely stubborn dogs.