Life in the 21st century is characterized largely by technology we have grown dependent upon. Perhaps the most ubiquitous of all tech devices are personal communication devices such as cell phones. Any new technology raises issues and with cell phones, the biggest seem to be privacy issues.
The National Security Agency (NSA) in the post-9/11 world has been granted sweeping powers to listen in on and spy on the private communications of citizens. In these times were we seem to be trading in all of our freedoms for "safety", the trend is definitely on the uptick.
How to Jam Cell Phones
Mobile phones use one band to send signal to their base station using an "upward signal" and another signal band to receive signal from the base station - the "downward signal". Cell phones can be jammed via interrupting any of these signals at a given point. Because the distance to base station is larger than the distance to mobile phone that needs to be blocked, it needs less energy to block signal from base station to phone.
The commercial hand-held cell phone jammers block frequencies between 800MHz to 1900MHz within a 30-foot range and carried can be used discreetly in a pocket or a handbag to block all cell phones in a small area.
Some academic institutions are currently rumored to be seeking the authority to jam cell phone transmissions because of "academic dishonesty". One could easily use one of these cell phone jamming devices in a public space such as an Internet cafe as well.
Most models above the 900mW range can block over a 30 foot area, while the more sophisticated jammers have the ability to block several types of networks at once. Jammers can broadcast on any frequency and are effective against AMPS, CDMA, TDMA, GSM, PCS, DCS, iDEN and Nextel systems.
With some of the systems that law enforcement and military can use, they can effectively shut down a city block, which is something that could be of strategic use during civil unrest such as the recent G20 riots in Toronto Canada. More and more terrorists are using explosive devices set of by the electronic detonation of PETN.
The Mossad in Israel were rumored to have assassinated a top Hamas leader by placing PETN in his cell phone which detonated upon his answering his phone. Since this trend is also on the upswing, authorities are using cell phone jamming technology to shut down things like presidential motorcades and similar events.
Police also frequently jam cell phones when conducting large raids on organized crime rings. Corporations are also using jammers to stop corporate espionage by blocking voice transmissions and photo transmissions from camera phones.
In most Western nations, it is illegal for citizens to jam cell phone signals, but some countries are allowing businesses and government organizations to use jammers where cell-phone use is seen as a public nuisance. Although it is illegal for a private citizen to jam cell phone signals, there apparently haven't been any prosecutions in the US for this.
It would be hard for the FCC to sniff out a jammer carried in your pocket as well. There are numerous places online where one can order a cell phone jammer for personal use. It might be one way to stop anyone from interrupting a live play or similar event where people create nuisances with cell phone.
There are also similar devices known as "cell-phone alerters" which can detect signals. There are no limit to creative uses of "cell phone vigilantes".