Jammers only affect the specified area

signal jammer work in one of two ways. Some devices set their signal to the same frequency as pagers and mobile phones, cutting off communication between handsets and base stations. Others work as electronic filters that fool mobile phones into thinking there are no frequencies available to make or receive calls. Manufacturers of the devices say the jamming only affects the designated area (most radii are a couple dozen to several hundred feet) and works only on cellular transmissions.

Last year, Algerian authorities asked isps (Internet service providers) to shut down social networks, but self-conscious measures alone were not enough to ensure enforcement. This year, says one security official, “Internet censorship will be better co-ordinated and more effective than ever”.Nouria Benghabrit, education’s minister, told Algerian media that the decision was “uncomfortable” but that they “should not be passive in the face of such a potential leak”.

But the sources told NBC that Russian’s sophisticated jamming equipment, which was developed by its military, has proved to be effective even against some encrypted signals and anti-jamming receivers.

American analysts first noticed the Russian military jamming drones in eastern Ukraine after the invasion of Crimea four years ago, Humphreys said. The jammers “had a pretty significant impact” on UN surveillance drones, which were grounded for days after gathering intelligence from the air. American military officials would not say whether the latest jamming has caused drones to crash, citing operational security.

The move to install the communication and radar jamming systems will strengthen China’s ability to assert territorial claims in the South China Sea and stop U.S. military operations in that region, which includes some of the world’s largest and busiest shipping routes.