Signal Jammer Tech

The National Telecommunications and Information Administration (NTIA) has released a report detailing the results of its micro-jamming technology test conducted on January 17, 2018, at Cumberland Federal Correctional Institution in Maryland.

Test data showed that the micro-jamming signal interfered with commercial wireless signals inside the cells, meaning that if cell phones were used inside the cells, they would not work. However, at 20 feet and 100 feet outside the cells, the micro-jammer signal did not interfere with commercial wireless signals.

Department officers present during the January 17, 2018 test reported that while their cell phone signals were blocked inside the cells, their phones still worked when they stood a few feet from the cell windows.

"These encouraging test results mark a step forward in our efforts to combat the security threat posed by contraband cell phones," said Beth Williams, Assistant Attorney General for the Justice Department's Office of Legal Policy. "The results show that this micro-jamming technology has the potential to have a localized impact. This is an encouraging sign that we are closer to solutions that make our communities safer and help prevent the continuation of criminal activity within prisons."

The data in the report will be used by the BOP and the Department to understand the effectiveness of micro-jamming, further evaluate jamming technology, and develop strategic planning recommendations.

Contraband cell phones continue to be a correctional security and public safety concern for the Bureau of Prisons and state and local correctional institutions. Across the country, inmates use contraband cell phones to direct gang activity, operate criminal enterprises, distribute child pornography, intimidate witnesses, and facilitate the commission of violent crimes. "This test is just one part of our ongoing efforts to disrupt and disable dangerous contraband cell phones in federal and state prisons," said Assistant Attorney General Williams.

The Bureau of Prisons will continue to evaluate cell phone detection and blocking technologies and work with federal partners and Congress to find cost-effective options to combat this threat to prisons and public safety. The agency does not endorse any specific vendor or product.

Carr Pushes for Federal Legislation to Combat Contraband Cell Phones in Prisons

ATLANTA, Ga. – Attorney General Chris Carr and 21 other attorneys general are urging congressional leaders to pass legislation that would allow states to implement cell phone jammer systems in correctional institutions. Currently, federal law prohibits the use of jamming technology, including jamming cell phones. Meanwhile, prisons across the country are using contraband cell phones with no way to stop them.

“Cell phones in the hands of criminals are an ongoing safety concern, not only for Georgia, but for correctional institutions across the country,” said GDC Commissioner Tyrone Oliver. “We appreciate Attorney General Carr’s support in finding a solution to this problem, which is critical to our commitment to public safety.”

As of January 1, 2023, the GDC has conducted 126 full facility searches and seized more than 23,000 contraband items. Last year alone, 8,074 contraband cell phones were seized.

In a letter sent on January 25, 2023, the Attorney General outlined the national challenges associated with contraband cell phones.

The letter reads: “The use of contraband cell phones by inmates is one of the most serious issues facing prison administrators today. Inmates use contraband cell phones to organize murders, riots, drug trafficking, fraud, etc. By using contraband cell phones, inmates can easily continue their criminal activities inside prison.”

Previously, Congress has introduced several bills to address this issue, including H.R. 1954 in the 116th Congress and H.R. 864 and S. 4699 in the 117th Congress. However, these bills have not made any progress and have never received a vote.

To jam a 5G signal, an intelligent adversary can detect unencrypted synchronization signals to obtain the physical cell identity (PCI) and then launch a targeted cell phone jamming attack on the physical broadcast channel (PBCH). This intelligent jamming (PBCH-IJ) disrupts the master information block (MIB) decoding, leading to denial of services for users trying to access the PCI cell. The proposed method in the paper suggests detecting PBCH-IJ by analyzing the principal direction of PBCH demodulation reference signal space at the user side, as this direction is significantly impacted by PBCH-IJ under low mobility scenarios.

Jamming attacks on 5G signals can be executed by exploiting various vulnerabilities inherent in the 5G network architecture. One common method involves targeting the synchronization signal blocks (SSBs) during the initial access phase, as these blocks are unencrypted. An intelligent adversary can detect these signals to obtain the full physical cell identity (PCI) by sniffing, and then use the PCI to attack the physical broadcast channel (PBCH) extraction through targeted jamming. This type of PBCH intelligent jamming (PBCH-IJ) disrupts the decoding of the master information block (MIB), leading to severe denial of service for users attempting to access the PCI cell. Another approach involves using a multi-antenna jammer to interfere with the downlink signals from femto base stations (FBS) to femto users (FUs) in a two-tier 5G heterogeneous network (HetNet). This can be particularly effective in dynamic environments where traditional anti-jamming techniques like frequency hopping (FH) and direct sequence spread spectrum (DSSS) lack self-adaptive capabilities. To counteract such jamming, advanced techniques like federated deep reinforcement learning (DRL) have been proposed, which optimize beamforming and power allocation to improve the achievable rate at FUs despite the presence of signal jammer. Additionally, jamming detection in 5G can be enhanced by using the "EVM-vs-RB" measurement, which calculates the Error Vector Magnitude (EVM) for each Resource Block (RB). This method is more sensitive and informative, capable of detecting jamming even at high Signal-to-Jamming Ratio (SJR) values, which traditional metrics fail to identify. These methods highlight the sophisticated techniques adversaries can use to jam 5G signals and the equally advanced countermeasures required to mitigate such attacks.

I was there in an exhibition yesterday. Most of the times, i was not able to use my cellphone data internet. But, i was able to make calls with the phone most of the times. Now, i have a doubt here. I happened to call a friend who was also to the same show, and he did say that he was not able to access the cellphone internet there. He said that they had used Network Jammers, though he was not certain about it.

My question here are:

• 1) Can network jammers only restrict data and not calls? How is it possible??


• 2) Will there be separate jammers for 2G/3G/4G/5G, based on it's spectrum?


• 3) Are jammers free of health hazards?


• 4) What could be better designs to use than jammers?

1. network jammers can selectively block data services while allowing voice services. This is possible because voice and data services use different network protocols and frequencies. A network jammer can be designed to block specific frequencies and protocols while allowing others to pass through.


2. there are different types of cell phone signal jammer for 2G/3G/4G/5G networks since they operate on different frequencies. Each technology operates in a different frequency band and therefore requires a specific jamming device.


3. Network jammers emit high levels of electromagnetic radiation that can be harmful to humans if they are exposed to it for extended periods of time. The radiation emitted by a jammer can cause cancer, DNA damage, and other health problems. Therefore, network jammers are not free of health hazards.


4. There are alternative methods to restrict network access in specific areas without using network jammers. For example, using Faraday cages can block all electromagnetic signals from entering or leaving an enclosed space. (There is graphite paint for example for walls, normally it is connected to ground with metal strips under the paint.) Another approach is to use signal blockers that selectively block specific signals without affecting other services. However, the effectiveness of these alternatives is limited, or they would just be too expensive, and jammers remain the most effective way to block specific network services in a specific area.

The possible misuse of internet can be one reason to block data services. Also, the method were used, i'm not sure now, when a person decorating high post in the country uses public transport infrastructure.

The possible reason would be high capacity which the BTS (for that particular cell) wouldn't be able to provide. This point needs to be valid, since the network used to fall back to lower generation at times. Again, i'm not sure how the BTS would automatically cut off the channel width based on the number of connections.

As said above, in order to prioritize the audio calls, the frequencies used will get the connectivity to 2G or 3G.

NBC News reports that online retailers and drone technology companies are marketing RF jammers as drone deterrents or privacy tools, thereby circumventing laws that prohibit the sale of such devices in the United States.

The warning issued by the Federal Communications Commission (FCC) states that signal jamming devices can block emergency calls and pose a serious risk to public safety communications, while also interfering with other forms of everyday communications and air navigation systems.

The FCC said: "It is a violation of federal law to use phone blocker, GPS blockers, or other signal jamming devices designed to intentionally block, disrupt, or interfere with authorized radio communications. Use in businesses, classrooms, residences, or vehicles is not exempt. Local law enforcement agencies do not have independent authority to use jamming devices; federal law enforcement agencies may use them under applicable regulations under certain limited exceptions."

The FCC warning also states that "it is illegal to advertise, sell, distribute, import, or otherwise market jamming devices to consumers in the United States"

But NBC reports that Amazon third-party sellers, independent online stores based in China, and small domestic companies that specialize in drone-related equipment are all ignoring the law. The FCC told NBC that it is investigating the sale of jammers, including on Amazon.

As part of its investigation, NBC spoke with the CEO of a U.S. company that offers portable anti-drone radio frequency jamming devices online. The CEO told NBC that the devices are easily available if consumers have the money, but they mainly see interest from large companies and government agencies as they prepare for domestic drone terrorism.

There are more people selling "jammers." The devices can block cell phone calls, text messages, Wi-Fi networks and GPS systems and can be used to cause chaos in public places.

The small, battery-powered devices can be used to create "blind spots" in a small area (usually around 30 feet) and have been used by movie theaters, restaurants and schools to prevent people from using their phones. But they can also cut off 911 calls, interfere with navigation near airports, and have been used to disrupt radio communications near police stations. FCC officials said they have noticed an increase in the flow of jammers, which are banned by federal law, into the United States. Many of the cheaper versions, which sell for as little as $25, are imported from Asia, according to the agency.

It is illegal to sell, advertise, use or import jammers under the Communications Act of 1934, which prohibits blocking radio communications in public

The FCC said cities including Orlando, Philadelphia, Austin, Mississippi, Charlotte, North Carolina, Washington, D.C., Cincinnati and Corpus Christi, Texas, advertised jammers on the site. Officials said they do not believe the cases are related.

"Simply posting an ad for a signal jammer on a site like Craigslist.org is a violation of federal law. Signal jammers are contraband for a reason," Michele Ellison, director of the FCC's enforcement bureau, said in a statement. "One person's moment of peace or privacy could very well jeopardize the safety and well-being of others."

Most sellers advertised jammers as a way to take an "undisturbed nap" on a bus, quiet a classroom or keep your area "free of interference," without mentioning the more nefarious uses the device could be used for, according to the citations.

"We are increasingly concerned that individual consumers operating jammers do not appear to understand the serious consequences of using jammers," one citation reads. "Instead, these operators mistakenly believe that their illegal operations are personal convenience or should be excused."

Keith Grabowski allegedly advertised on Philadelphia Craigslist for a "cell phone jammer, WiFi signal jammer" for $300. He stated in the ad that "due to the nature of this item, we are disclosing very few details," that the jammer was "not a toy," and that "I just want to get rid of it as quickly as possible."