The Havahart Remote Trainer Extra Collar only works with the Havahart Remote Trainer. Unlike many remote trainer options, the Havahart Remote Trainer can operate two collars, training two dogs at once (with Remote Trainer Extra Collar). Additionally, each collar can be set to its own static correction level, allowing flexibility for the temperament of each dog. When you press the Correction button, a static stimulus is sent to the collar and a correction is delivered. If you wish to use tone only to control behavior, simply press Warning. Your dog will hear a tone and will begin to associate the tone to the misbehavior. As a safety feature, the unit automatically shuts off and correction is stopped if a button is pressed and held for 10 seconds. To protect your dog, please observe the following safety precautions: Never leave the collar on your dog for more than 12 hours at one time. Pressure Necrosis, which can severely irritate a dog"s skin, is caused by extended pressure of the probes on skin, along with oil/dirt that accumulates on the probes. Check daily for skin irritation. Only use the Remote Trainer on healthy dogs, ages 6 months and older. Consult your veterinarian before using if your dog has health problems. Check collar fit each time you place collar on your dog– the collar must be fitted properly to work effectively. If the collar probes are not making complete contact with the dog"s skin, the trainer will not work to its full effectiveness. Always use the lowest stimulation possible to train your dog.