The system works by delivering a safe static correction through two contact points that touch your pet's neck. If your pet crosses the established boundary zone, a static correction will get your pet's attention but will not hurt him. The Free to Roam receiver collar includes 5 levels of static correction plus tone only adjustable to your pet's temperament. With just a few short training sesions, you'll create a secure boundary for your pet to enjoy freedom and fun. The fence works with multiple pets as long as they are wearing a compatible PetSafe wireless receiver collar. The waterproof receiver collar is ergonomically designed for comfort and sized for pets weighing 5 pounds or more.