Your metal building is a faradays cage for cell signal, it is a good thing!

A Faraday’s cage is a cage made of conductive material such as iron, copper or any other conductive material that shields an object from static or electromagnetic signals. Basically its like how ozone layer protects the earth from harmful ultraviolet rays. It is a good thing in most cases but not when it comes to cell phone signal. Buildings constructed with metal studs or frames are great for structural integrity not so great for cell phone signals. However the signal that does not get IN due to a metal structure , also does not let the signal OUT once it is inside the building, making it a desirable outcome when using cell phone signals.

A cell phone repeater systems turns a undesirable metal structure into a desirable outcome. The call phone repeater system consists of three major components. The outside antenna, inside antenna and an amplifier. The amplifier is the driving engine of the cell phone booster system. The exterior antenna seeks weak cell phone signal in the location and transfers it inside the building via cable to the amplifier. This is the key to overcoming week signal that has trouble getting into buildings that have a metal structure. The cable acts as the conduit for the signal to get into the building. Once the signal in inside the building, it is amplified by the amplifier and then distributed throughout the whole inside.

A fun video :