First of all, I must admit that you are half right. Because the jamming device is not yet fully legal in the world.
Because different countries have different policies for jamming devices.
For example, jamming devices in China and Japan can be used in education institutions. Some European countries, such as France and Britain, allow jammers to be used in cinemas, libraries and other places. In the United States, some state prisons are already using cell phone jammer.
Therefore, it cannot be said that jamming devices are legal or illegal. It depends on what kind of country and region you live in