A mobile device includes a receiver for receiving radio frequency (RF) signals from a signal generating unit of an invisible fence system when a user reaches or enters a zone defining a pet restricted area. The mobile device can identify a frequency of the signals which were received from the signal generating unit. The mobile device can notify a user by providing a warning regarding the presence of the invisible fence system based upon identification of the signals. The mobile device also includes a transmitter for emitting RF signals at the identified frequency of the invisible fence system defining another zone surrounding the mobile device and the user.
