A cell phone jammer is a device used to block cellphone signals between cellur phones and towers, preventing mobile phone users from making and receiving calls.

Why would you want one? Well we have all encountered that inconsiderate someone who in the movie theater, restaurant or where have you, continues to yap away regardless to the consideration of others.

While most of us just grumble under our breath, some are taking matters into their owns hands and purchasing a yapper zapper

The cellphone jammer works by transmitting a signal on the same radio frequency used by the mobile phone. The signals sent out by the cellular jammer and the phone collide to simply cancel each other out.

The now jammed phone will indicate that there is no service or no network signal. Mobile phones are full-duplex devices, which means they use two separate frequencies, one for talking and one for listening simultaneously.

Some jammers block only one of the frequencies used by cell phones, which has the effect of blocking both. The phone is tricked into thinking there is no service because it can receive only one of the frequencies.

Less complex devices block only one group of frequencies, while sophisticated jammers can block several types of networks at once to head off dual-mode or tri-mode phones that automatically switch among different network types to find an open signal. Some of the high-end devices block all frequencies at once, and others can be tuned to specific frequencies.

To jam a mobile, all you need is a device that broadcasts on the correct frequencies. Although different cellular systems process signals differently, all cell-phone networks use radio signals that can be interrupted. GSM, used in digital cellular and PCS-based systems, operates in the 900-MHz and 1800-MHz bands in Europe and Asia and in the 1900-MHz (sometimes referred to as 1.9-GHz) band in the United States.

Jammers can broadcast on any frequency and are effective against AMPS, CDMA, TDMA, GSM, PCS, DCS, iDEN and Nextel systems. Old-fashioned analog cell phones and today's digital devices are equally susceptible to jamming.

The cell phone jamming device, oftentimes disguised as a typical mobile phone will block cell phone signals within a range of up to 30 feet. Sometimes refereed to as a cell phone blocker they where developed originally to allow law enforcement officials to interrupt communications by criminals.

A cell phone jammer is ideal for meeting rooms, conference rooms, museums, galleries, theaters, concert halls, churches, temples, restaurants, classrooms, training centers, factories, banks, trains, buses etc or if you want to avoid information being disclosed secretly during meeting and anywhere else you need peace and quiet.