Cell phone jammer
From Wikipedia, the free encyclopedia
A cell phone jammer is an instrument used to prevent cellular phones from receiving and transmitting the mobile signals to a base station. When used, the jammer effectively disables cellular phones in the area. These devices can be used in practically any location, but are found primarily in locales where a phone call would be particularly disruptive. These include churches, mosques, libraries, movie theaters, meeting rooms, and other places where silence is expected.
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[edit] History
The rapid proliferation of cell phones in recent years to near ubiquitous status eventually raised problems such as their potential use to invade privacy, contribute to academic cheating, or even aid in corporate espionage. In addition public backlash was growing against the perceived disruption cell phones introduced in daily life. While older analog cell phones often suffered from chronically poor reception and could even be disconnected by simple interference such as high frequency noise, increasingly sophisticated digital phones have led to more elaborate counters. Cell phone jamming devices are an alternative to more expensive measures against cell phones, such as Faraday cages, which are mostly suitable as built in protection for structures. They were originally developed for law enforcement and the military to interrupt communications by criminals and terrorists. Some were also designed to foil the use of certain remotely detonated explosives. The civilian applications were apparent, so over time many companies originally contracted to design jammers for government use switched over to sell these devices to private entities. Since then, there as been a slow but steady increase in their purchase and use especially in major metropolitan areas.
[edit] Operation
Jammers block cell phone use by sending out radio waves along the same frequencies that cellular phones use. This causes enough interference with the communication of cell phones and the towers to render the phones unusable. On most retail phones, the network would simply appear out of range. Most cell phones use different bands to send and receive communications from towers. Thus jammers can work by either disrupting phone to tower frequencies or tower to phone frequencies. Smaller handheld models block all bands from 800mhz to 1900mhz within a 30 foot range. Small devices tend to use the former method, while larger more expensive models may interfere directly with the tower. The radius of cell phone jammers can range from a dozen feet for pocket models to kilometers for more dedicated units. The TRJ-89 jammer can block cellular communications for a 5-mile (8 km) radius. [1]
Older jammers sometimes were limited to working on phones using only analog or older digital mobile phone standards. Newer models such as the double and triple band jammers can block all widely used systems (AMPS, iDEN, GSM, et al) and are even very effective against newer phones which hop to different frequencies and systems when interfered with. As the dominant network technology and frequencies used for mobile phones vary worldwide, some work only in specific regions such as Europe or North America.
The power of the jammer's effect can vary widely based on factors such as proximity to towers, indoor and outdoor settings, presence of buildings and landscape, even temperature and humidity play a role.
There are concerns that crudely designed jammers may disrupt the functioning of medical devices such as pacemakers. However, like cell phones, most of the devices in common use operate at low enough power output (<1W) to avoid causing any problems.
[edit] Legalities
Since these jammers actively broadcast radio signals they may (or may not) be legal to possess or operate based on the specific laws of the area you're in.
- Australia: Illegal.
- Belgium: Illegal to sell, possess and operate (licensed part of the spectrum).
- France: France legalized cell-phone jammers in (movie) theaters, and other places with performances in 2004.
- India: Government and school use jammers.
- UK: Illegal.
- USA: Illegal to operate, manufacture, import, offer for sale, including advertising (Communications Act of 1934)[2] with fines of up to $11,000 and imprisonment of up to a year.
This is not legal advice, seek professional help as needed.
