Cell phone repeaters are becoming common fixtures inside commercial buildings. They are used to pull cellphone signals from the outdoors to the inside of a building. Indoor cellphone repeaters often have an outdoor antenna to receive and transmit signals from a nearby cell tower. The outdoor donor antenna is usually connected to an amplifier that increases the cellphone signal. The increased signal is then distributed throughout the building interior with one or more indoor antennas, providing improved cellphone signal strength inside the building.