With PetSafe's indoor radio fence, you can choose a range inside your home that you want your pet to avoid. When your pets receiver collar strays into an area thats 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.