The FieldTrainer 425 Remote Trainer works by using the Remote Transmitter to communicate with your dog’s rechargeable Collar Receiver. From up to 500 yards away, it can send a signal in the form of a safe, static interruption, tone, or vibration to correct/communicate with your dog. DryTek™ waterproof and submersible to 25 fee, so you don't have to worry about taking the colllar off when your dog gets a bath or goes swimming. You can even expand your training with additional collars, up to three dogs at once! Gun Dog Magazine called it "Flawless Design"