an in - building communications system is disclosed which permits communication in tunnels , underground parking garages , tall buildings such as skyscrapers , buildings having thick walls of concrete or metal , and / or any building which has communication dead zones due to electromagnetic shielding . the invention includes a portable bi - directional amplifier system , an outdoor antenna system attached to the building or independently mountable an indoor antenna system attached to the building or independently mountable inside the building , and a standardized , in - building communications interface box affixed preferably to the exterior of the building . the interface box communicates with antenna systems attached to the building . the fire department or other emergency response personnel carry portable outdoor and indoor antenna systems and a portable , lithium - ion battery powered , bi - directional amplifier system which may be connected to the building during an event such as a fire , earthquake , or an act of terrorism or whenever radio coverage enhancement is required . the portable bda system is simply connected to the standardized , ibc interface box and powered thus restoring communications within .