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What is a Cell Phone Jammer?

By R. Kayne
Updated May 16, 2024
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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 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 good 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 grocery stores, shopping malls 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 jammer in purse or pocket, phones can be turned off with the flip of a switch — and they won't be able to reconnect as long as the device is activated, unless they move far enough away from the source.

It seems a tidy solution, however, there's a problem. Cell phone jammers are illegal in most countries, except to military, law enforcement and certain governmental agencies.

In the U.S. the FCC (Federal Communications Commission) makes certain frequencies available to broadcasters for public use. When an end-user pays to use that spectrum, jamming the signal is paramount to property theft. The FCC is also concerned about potential "leakage," jammers interfering with frequencies outside the range of cell phones, like garage door openers or medical equipment. It's worth noting that over 100,000 emergency calls are made each day from cell phones. Anyone caught manufacturing, selling, owning, or using a jammer in the U.S. may be punished with a fine and up to a year in prison for each offense.

The stiff penalty hasn't stopped proliferation of the devices, perhaps because the FCC has not held anyone accountable. This isn't surprising considering people can't tell the difference between being jammed and simply having poor signal strength that comes and goes with the best of phones even under normal circumstances.

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 devices. While personal ones create a bubble of anywhere from 30 to 100 feet (9 to 30 meters) depending on the model, more powerful devices can create "dead space" of up to 1 mile (1.6 km) in radius. This can be useful around a presidential motorcade, for example, to keep terrorists from detonating a bomb from miles away or even from outside the country. By wiring a cell phone to explosives, the device can be triggered by simply placing a call to the phone, as was done in May 2002 by Palestinian militants in Tel Aviv when they targeted an Israeli fuel depot by rigging one of its fuel trucks.

Law enforcement also uses these devices in hostage situations to keep the suspect isolated, and in South America, banks use the devices to prevent robbers from tipping off outside accomplices to departing customers leaving with large withdrawals.

Proprietors of many kinds of businesses would like to use cell phone jammers. Restaurant owners and theater houses are just two examples of places that regularly receive complaints from patrons over cell phone abuse. Short of providing expensive metal shielding in the construction of the buildings to block cell phone signals — which is legal — it's understandable that placing an inexpensive device in the back office to surreptitiously block cell phone usage in the establishment might be tempting. Hospitals would also like to jam cell phones that might interfere with medical equipment. Churches, libraries, courthouses and business owners that want to boost employee productivity are all examples of potential customers of cell jamming technologies.

The top manufacturers reportedly sell jammers primarily to military and law enforcement, but they will sell the devices to anyone with the disclaimer that it is up to the buyer to make sure the device is legal in his or her country and that the buyer assumes all legal responsibility for buying, owning, or using the device. The cell phone industry opposes the use of these devices, and many have invested money in education towards cell phone etiquette as an alternative answer to the growing problem of discourteous cell phone users.

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Discussion Comments

By anon269864 — On May 20, 2012

It says that jammers can be useful to avoid cellphone usage near some equipment or places. And the idea is that the cellphone's radiation would interfere with the equipment. But how does it help to have a perpetual radiation of a jammer, since that radiation could be interfering with the devices as well.

For example, using jammers in hospitals to avoid interference with medical equipment.

By anon256974 — On Mar 24, 2012

Take a look at this application in the Android Market. It's called Anti Jammer and it's made to sound an alarm when your mobile is loses coverage. It's useful if you've an gsm alarm system at your home under a possible intrusion.

By anon255181 — On Mar 16, 2012

They are great fun to use and annoy people. Just get your supplier to pull it apart and say it's spare parts. That's how people get them in.

By anon249036 — On Feb 19, 2012

My students are constantly texting in my class. I write them up but it does not stop them. I was going to buy a jammer until I found out it is illegal. What a bummer!

By mallin — On Jul 18, 2011

I hit upon a site that sells jammers the other day. and I bought a portable cell phone jammer, and it's working great.

By anon161248 — On Mar 18, 2011

is there a way to stop the jammers? some jam wireless security cameras, wifi and cell phones as well. i have a neighbor who is stalking us and is using a jammer to stop all of our connection to the outside world, security cameras against her and kids internet for schooling purpose. it is dangerous and scary. Cops won't do anything. please help, does anyone know how to stop a jammer?

By anon159035 — On Mar 09, 2011

But how can I make them legal in the U.S.?

They should be used in classrooms, prisons and meeting rooms. Think of how much teachers would benefit from the ability to curb distracting texting during class?

By anon156703 — On Feb 28, 2011

Firstly there is no way to defeat jammers because you need to spread more a dominant signal (with the same frequency band) then the jammer's signal for defeating it but in this situation you are going to affect your device too.

As a result, your device won't work which means the jammer still does its work even if you defeat it. İ have one question too. As i know, jammers affect carrier signal of s(t). But every message signal has a different carrier signal. How can a jammer dominate every kind of carrier signals?

By anon63002 — On Jan 29, 2010

Not usually, since the jammer signals are much stronger than the signals the phones are trying to receive. There's no special techniques, the phones are simply overloaded.

By anon62985 — On Jan 29, 2010

A cell phone jammer is a great device and I use it almost every day to protect my privacy.

By anon61687 — On Jan 21, 2010

As a teacher, I was excited to think I could use a jammer in class to stop the blatant disregard for school rules. Alas they are illegal, not worth the risk to career.

By anon61242 — On Jan 19, 2010

I bought a jammer. it is very good, I love it!

By anon56818 — On Dec 17, 2009

Unfortunately jammers are easy to locate as they affect so many users at the same time which shows up as a spike in dropped calls off a particular cell site.

Engineers don't like to see dropped call stats spike and because all phones have a GPS it's easy to find out where the drops are occurring.

Since jammers are illegal your $250 jammer will be confiscated. Use it intermittently and never in the same building for more than a few days.

By anon42321 — On Aug 20, 2009

I bought a cell phone jammer on-line from infostream, great gadget. I love it

By jammer01 — On Mar 30, 2009

Why are cell phone jammers illegal in most countries?

I bought a pocket size cell phone jammer SK-16A and a medium power cell phone jammer SK-3. They are very good and help me block the annoying phone calls in the library, lab, meeting room, and hospital. I think jammers are very helpful.

By anon9815 — On Mar 14, 2008

How does WIMAX system work?

By anon4929 — On Nov 06, 2007

I know this device is illegal but it could be useful to avoid that annoying people who insists in disturbing our silence...

By fallentech — On Jul 18, 2007

IS there a known way to defeat the jammers?

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