Jammers can prevent students from playing mobile phones under certain circumstances As I said before, these signal blocking devices, including GSM jammers and WiFi blockers, have been used in many countries around the world. But it's best to read some information about how these jammers work. Another important piece of information to know is which signal interception devices are used. Many people use these signal jammers, so we tried to develop some simple principles to use jammers safely without harming anyone.In the United States, there is no restriction on the use of interfering equipment, but broadcasting on specified frequencies is prohibited without permission. https://www.jammer-buy.com/gsm-jammer/c-26.html