This is how the main secure data centers in the US are built You may have cell phone reception at the visitor's center before registering due to (in rare cases) glass windows or you are not allowed to bring cell phones, but as soon as you enter safe areas that are usually walls reinforced concrete, with some with additional RF shielding and / or metal walls, little or no reception is obtained, as many are designed with very high safety standards to adapt to the high safety requirements of the top. public and private sector. For those who normally need the ability to connect to wireless communications (4G, LTE, satellite, microwave, etc.), many will be downloaded to the ceiling or to a separate location that will receive a good signal if available.
The signals from cell phones have difficulty passing through very thick reinforced concrete walls due to the reduction in the amount of radiation that can pass through them (attenuation). Some do it by accident while trying to make sure that the walls are reinforced and thick (the same happens if you put a metal tent in the windows of your car and there are too many metal particles in it). With many data centers, metal rooms / doors reduce the signal of the cell quite well to the point that it does not receive a signal (without bars). This is even a major problem in multi-story office buildings and apartments the closer you get to the center of the building, especially if it is a building with little or no window (for example, many secure government office buildings, government contractor offices). , ISP data centers). , DR purpose data centers, etc.).
If you get a strong signal, it is most likely that you are not in a high security data center, which is fine if your business does not require high security. In many high-security data centers, you should get a good cold and hard response from the thick reinforced concrete walls if you hit them with your knuckles with little or no noise (in addition to the sound of your knuckles striking the wall) after to pass. Through a nice heavy metal secure controlled access door.