With our indoor radio fence, you can choose a range inside your home that you want your pet to avoid. When your pet’s receiver collar strays into an area that’s off-limits, he receives a warning tone followed by a mild stimulation to remind him to move back into the safe zone. Best of all, if you already have a PetSafe® outdoor in-ground fence, the same receiver works inside. Plus, the system can be used with an unlimited number of pets, with each wearing their own receiver collar. Indoor Radio Fence does not include receiver collars; works with any PetSafe in-ground fence receiver collar sold seperately.