Hello! The invention of the mobile phone has become the 21st century's most famous, mobile devices and intelligence to make it very popular, but in some places, it doesn't seem to be too popular, even need to ban the use of it, such as the examination room need to ban mobile phones, is to prevent cheating. So why does the secret service ban cell phones? What all these places have in common is the installation of a cell phone jammer
to stop it.