Telephone signal jammers are mainly used in places where the use of mobile phones is prohibited, such as examination rooms, schools, gas stations, churches, courts, libraries, conference centers (rooms), theaters, hospitals, government, finance, prisons, public security, military places, etc. It is understood that the mobile phone signal jammer on the market can limit the distance of the mobile phone signal from the transmitter to 500M. https://www.greatjammer.com/cell-phone-jammer-c-1.html