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A cell phone jammer is a piece of equipment capable of blocking reception or transmission of cell phone signals. This is mostly done by creating some form of interference at the operating frequency ranges of cell phones, which results in no signal or significant loss of signal quality. Although cell phone jammers could be used practically anywhere, they are mainly used in areas where silence is expected or required.
A cell phone jammer consists of:
When a cell phone jammer is active, most cell phones show no network signal, and when the cell phone jammer is switched off, the cell phone becomes active. Cell phones use unique frequencies for talking and listening. Most cell phone jammers block either of the two frequencies, indirectly providing the effect of prevention of both. Cell phone jammers work on the same principles as that of jammers used in preventing radio communication. They either function by disrupting the cell-phone-to-base-station frequencies or base-station-to-cell-phone frequencies.
Cell phone jammers are used by law enforcement and military to limit and disrupt communications during various situations. Certain organizations use cell phone jammers to prevent corporate espionage by blocking communication within sensitive areas. Portable cell phone jammers are also used by some people to prevent others from using cell phones in their immediate vicinity.
Apart from military and law enforcement applications, cell phone jamming is illegal in many countries, including the United States. U.S. law bans the sale or purchase of cell phone jammers, and has some of the strictest laws in the world regarding their usage. Some countries such as Mexico allow use of cell phone jammers in public areas such as hospitals. Different countries have different laws regarding the use of cell phone jammers.