Tuesday, January 24, 2012


• In China the Education Department uses mobile jammers in schools during major exams. These jammers are use to prevent cheating. The objective is to prevent students from receiving calls or SMS messages from external sources outside the exam room.
• The main electronic components of a jammer are:
1)Voltage-Controlled Oscillator - this generates the radio signal that will interfere with the cell phone signal.
2)Tuning circuit - controls the frequency at which the jammer broadcasts its signal by sending a particular voltage to the oscillator.
3)Noise Generator - Produces random electronic output in a specified frequency range to jam the cell-phone network signal.

Safaricom and Kenya Prisons Services recently announced that they will install phone-jamming equipment in all the major prisons. This was termed as a response to the runaway crime involving mobile phones that is perpetuated by prisoners.
The strategy of jamming mobile phone signals in prison compounds is a logical technical response. By creating islands of non-connectivity in these jails, it is possible to mitigate the economic and social risk posed by these incarcerated criminals.

How does mobile jamming work?

Phone jamming is not a new phenomenon. In the past it was associated with spy craft and the military. Times have changed. Mobile phone jammers are now commercially available and widely used by ordinary citizens in countries that have legalized their usage.

Jamming a mobile phone basically entails the blocking of its frequency by using a device called a jammer. Your mobile (short for mobile phone) transmits a signal on a certain frequency so as to communicate with the service provider’s network. The jammer will broadcast a signal to your mobile using this very same frequency. Once these two signals collide they cancel each other out and what results is a ‘No Network’ indicator on your mobile.

The range of a jammer depends on its power output and whether it is designed to disrupt mobiles or towers. Pocket/portable jammers typically operate in a range of about 9 meters. Higher powered jammers operate in a range of up to 1.6 kilometers away from the device.

The choice of which jammer to use is dependent on the range you wish to deploy it to. To have uninterrupted meetings in an enclosed room, portable jammers are ideal. In a restaurant or church, a medium power jammer would suffice. For a prison compound, a very high powered jammer that can block multiple frequencies would be the ideal.

Mobile Jamming Concerns

It is broadly agreed that something needs to be done to curb the acquisition of mobile phones by criminals in our local prisons. However the jamming of mobiles has been tried by other countries with varied success.

Of initial concern would be the fate of prison staff and family who live and work in these compounds. To be able to effectively jam mobiles in our expansive prisons, high powered jammers will have to be used. This means that prison staff and other mobile users in the surrounding areas will also be inconvenienced.

Interference with critical public frequencies is another risk. Public safety responders like ambulances, police and fire fighters use dedicated frequencies. High powered jammers should be configured to ensure these frequencies are not interfered with.

It is also worth considering the legality of this implementation. The Kenya Information and Communications Act – Section 45 states that interference with any radio communication would result in a fine not exceeding one million shilling or a prison term not exceeding five years or both.

Other Alternatives

Combating the use of mobile phones by prisoners to propagate crime requires a multi-pronged approach. Jamming their mobiles, in itself, is not enough.

We should start by increasing the criminal penalty of smuggling mobiles into our prisons. The penalty for this kind of crime should be extremely punitive so as to discourage prison staff and visitors from abetting the smuggling of mobiles.

Other technical measures that should be explored include handset disablers, micro-cells and Faraday cages.

Unlike jammers, handset disablers do not emit jamming signals. They instead detect the presence of mobiles and prevent the making of any call. This detection and disabling is done by the software at the base station. What makes this alternative attractive is that it does not disable calls from ‘emergency users’. Pre-selected mobile users, who have pre-registered their phone numbers with the service provider, are allowed to receive and make emergency calls.

Micro cells are essentially scaled down base stations. It would be possible to build micro cells dedicated to the prisons. These cells would carry all traffic originating and terminating in the prison compound. In this implementation it is possible to segregate only prison calls and avoid jamming calls of legitimate users in the prison environs. The micro cell would be able to intercept communications specific to the prison and disable the mobiles through either SIM or IMEI blocking.

Another alternative is the Faraday cage which is a wire mesh enclosure that is grounded. It provides a shield to radio waves. A cage round the main prison compound would impede the transmission of mobile phone signals to or from any handset located in the cage.

Critical Lesson

One critical lesson that needs to be internalized from this effort is that there is a slow but sure shift from conventional to cyber crime by Kenyan criminal elements. The ingenuity and innovativeness exhibited in the execution of these mobile phone scams proves that it is only a matter of time before ICT security becomes a priority for law enforcement agencies.


Handset Detection said...

Hello Dude,

Every jamming device has an antenna to send the signal. Some are contained within an electrical cabinet. On stronger devices, antennas are external to provide longer range and may be tuned for individual frequencies. Thanks for sharing it.......

Muthoga Kioni said...

Thanks for your comment Handset Detection. You point is duly noted.

cell phone jammer said...

A cell phone jammer is a device used to block cell phones from receiving signals from base stations & it is very helpful for us.