The Extra Collar for the Houndware HW777 Rechargeable Remote Dog Training Collar serves as the receiver unit for this training system. If you've misplaced or experienced damage to your current receiver unit, this collar provides a convenient replacement option. By acquiring this collar, you can seamlessly continue utilizing the Houndware HW777 Rechargeable Remote Dog Training Collar. The system is specifically crafted to assist you in effortlessly training your dog to reduce excessive barking.