Cell phone jammers and their uses - written by David McDaniel

A Cell Phone Jammer is a device that emits signals in the same frequency range that cell phones use, effectively blocking their transmissions by creating strong interference. Someone using a cell phone within the range of a jammer will lose signal, but have no way of knowing it was the reason. The phone will simply indicate poor reception strength.
With the ubiquitous use of cell phones, a backlash has occurred. While some people practice cell phone etiquette, many others noisily discuss their private, professional or mundane business in public areas, forcing everyone nearby to listen. On trains, subways, buses, in the grocery market, shopping mall and cafes, people are aggravating fellow citizens with their non-stop chit-chat. This has caused some people to take matters into their own hands. With a cell phone jammer in purse or pocket, jabber mouths can be turned off with the flip of a switch - and they won't be able to reconnect as long as the jammer is activated; unless they move far enough away from the source.
These Cell Phone Jammers are available in different styles and sizes, from personal hand-held models that look like cell phones themselves, to units that resemble routers with multiple antennas, to even larger briefcase-style jammers. While personal jammers create a bubble of anywhere from 30 - 100 feet (9 - 30 meters) depending on the model, more powerful devices can create "dead space" of up to a mile (1.6 km) in radius.
Personal cell phone jammers start at about $250 (U.S.D.) and are widely available online despite their questionable legal status in most countries. The top manufacturers reportedly sell primarily to military and law enforcement but will sell the devices to anyone, with the disclaimer that it is up to the buyer to assume all legal responsibility for buying, owning, or using the device.
The cell phone industry opposes the use of jammers and many have invested money in education towards etiquettes of a cell phone as an alternative answer to the growing problem of discourteous cell phone users.

Cell phone use has skyrocketed, making it hard to avoid hearing half a conversation in many public places. A small solution, becoming very popular worldwide, is the Cell Phone Jammer, a gadget that renders nearby mobile devices impotent. The technology is not new, but overseas exporters of jammers say demand is rising.
The jamming technology works by sending out a radio signal such that phones are overwhelmed and cannot communicate with cell towers. The range varies from several feet to several hundred yards, and the devices cost from $250 and up for quality models. Larger models can be left on to create a no-call zone.
The main electronic components of a jammer are:

# Voltage-controlled oscillator - Generates the radio signal that will interfere with the cell phone signal
# Tuning circuit - Controls the frequency at which the jammer broadcasts its signal by sending a particular voltage to the oscillator
# Noise generator - Produces random electronic output in a specified frequency range to jam the cell-phone network signal (part of the tuning circuit)
# RF amplification (gain stage) - Boosts the power of the radio frequency output to high enough levels to jam a signal

The Power supply
The smaller jamming devices are operated through the battery only. Some look like cell phones and use cell-phone batteries. Stronger devices can be plugged into a standard outlet or wired into a vehicle's electrical system.