The events of 9/11 taught some very valuable lessons.  One of the biggest was that the inability to communicate between first responders outside and inside may have cost lives.

In order to ensure the ability of first responders to effectively communicate, we measure the signal level of radio frequencies inside of structures.  If the signal level is high enough for radio communications to take place, generally, nothing more is needed.  If the signal levels are too low to be able to guarantee communications, we add a repeater, or BDA (Bi-Directional Amplifier) to amplify the communications channel into and outside of the building.