Here you can find your own jammer

I was there in an exhibition yesterday. Most of the times, i was not able to use my cellphone data internet. But, i was able to make calls with the phone most of the times. Now, i have a doubt here. I happened to call a friend who was also to the same show, and he did say that he was not able to access the cellphone internet there. He said that they had used Network Jammers, though he was not certain about it.
My question here are:

• 1) Can network jammers only restrict data and not calls? How is it possible??


• 2) Will there be separate jammers for 2G/3G/4G/5G, based on it's spectrum?


• 3) Are jammers free of health hazards?


• 4) What could be better designs to use than jammers?

1. network jammers can selectively block data services while allowing voice services. This is possible because voice and data services use different network protocols and frequencies. A network jammer can be designed to block specific frequencies and protocols while allowing others to pass through.


2. there are different types of cell phone signal jammer for 2G/3G/4G/5G networks since they operate on different frequencies. Each technology operates in a different frequency band and therefore requires a specific jamming device.


3. Network jammers emit high levels of electromagnetic radiation that can be harmful to humans if they are exposed to it for extended periods of time. The radiation emitted by a jammer can cause cancer, DNA damage, and other health problems. Therefore, network jammers are not free of health hazards.


4. There are alternative methods to restrict network access in specific areas without using network jammers. For example, using Faraday cages can block all electromagnetic signals from entering or leaving an enclosed space. (There is graphite paint for example for walls, normally it is connected to ground with metal strips under the paint.) Another approach is to use signal blockers that selectively block specific signals without affecting other services. However, the effectiveness of these alternatives is limited, or they would just be too expensive, and jammers remain the most effective way to block specific network services in a specific area.

The possible misuse of internet can be one reason to block data services. Also, the method were used, i'm not sure now, when a person decorating high post in the country uses public transport infrastructure.
The possible reason would be high capacity which the BTS (for that particular cell) wouldn't be able to provide. This point needs to be valid, since the network used to fall back to lower generation at times. Again, i'm not sure how the BTS would automatically cut off the channel width based on the number of connections.
As said above, in order to prioritize the audio calls, the frequencies used will get the connectivity to 2G or 3G.