One idea to deal with the problem of eavesdropping, apart from detection, is jamming. You can find many ‘miracle’ solutions on the internet that ‘guarantee’ security. Is this really the case? In the following section, we will point out the different types of jamming devices, how they work, and how effective such solutions are. We answer the question of how to jam a wiretap.
What are the popular eavesdropping solutions?
There are many different eavesdropping devices available on the civilian market, but they can all be assigned to one of 2 categories:
- Recording devices – voice recorders
- Transmitting devices – bugs
- analogue eavesdropping transmitters
- digital eavesdropping devices
- using GSM, UMTS, LTE
- having access to WiFi, sending to FTP or to the cloud.
- Wired eavesdropping devices – probe
The common denominator of all eavesdropping devices available to the ordinary Joe is that they have a microphone. For more information on how wiretaps work, see the post How does a wiretap work?
James Bond-style wiretaps
The most sophisticated eavesdropping solutions are those that do not require the direct presence of an eavesdropper in a room. It is possible to eavesdrop through a wall or glass using seismic eavesdroppers. These eavesdroppers applied to a surface pick up the micro-vibrations caused by sound waves and then amplify them so that the conversation can be heard.
Another option is the use of directional microphones, which, if directed at a person or an open window, allow the conversation to be heard from a distance under good conditions. Another solution for eavesdropping from a distance is the laser microphone. By directing an invisible laser beam, e.g. at a window pane, it is possible to hear everything that is happening in the room.
The eavesdropping device that requires the most interference in the room for installation is the probe. A probe is nothing more than a microphone placed on a cable. This type of eavesdropping allows live listening or recording of conversations outside the surveillance room. Due to the required high level of access to the room, this solution is not popular, but it is extremely difficult to detect. Is it possible to jam such an eavesdropper? – Yes, by affecting its microphone.
How to jam a wiretap? – effectively
Depending on the eavesdropper used, there are two ways to block or significantly reduce its operation. One can attempt to block the transmit and receive functions by jamming the radio signals, or one can block the operation of the microphones themselves. Both approaches have their limitations, which I list below.
Radio jamming
In order to block the operation of eavesdroppers sending information by radio, we are forced to use so-called jammers. These devices were available in many online shops until a few years ago, but the legislator restricted the possibility of trading jammers.
One of the reasons why the use of RF jammers is undesirable is that they interfere with mobile telephony and thus potentially prevent third parties from calling, for example, the ambulance or fire brigade. Jammers also block surrounding WiFi networks by breaking the internet connection to everyone within their range. ‘Victims’ of working jammers can also fall victim to gate controls, ventilation systems or wireless mice.
Jammers have another potential disadvantage that can adversely affect their effectiveness. These devices are usually ‘Chinese-made’, and thus even products of sufficiently high quality may jam frequencies that are not exactly the same as those used in Poland.
The user of a radio jammer can never be sure whether the signals he or she intended to jam are being jammed. He also does not know whether all signals are being jammed or perhaps none. Operating range is also a lottery – in cities, the density of BTS installations makes even the most powerful Chinese jammers inadequate.
The use of radio jammers does more harm than good. The level of effectiveness is judged to be far from acceptable, and the fact of coming into conflict with the law by blocking reserved frequencies lowers the overall rating of this type of solution to 0/10. We discourage the purchase and use of wireless jamming devices.
Microphone jamming
Everyone has probably heard of skimmers. The colloquial name of ultrasonic jammers probably comes from the fact that these devices generate sounds at the human ear’s hearing limit of 14 – 20 kHz. When a skimmer is triggered, younger people hear an unpleasant screech/noise, while people aged around 40 years and older hear nothing. The operating principle is simple. The scrambler is designed to generate high sound pressure that will stifle the microphones, making it impossible to record the conversation in progress. The noise generated is practically out of hearing and therefore does not disturb the callers.
In practice, however, older voice recorders with microphones with sensitivity characteristics below 14 kHz (e.g. magneto-electric microphones) prove largely insensitive to such jamming. Furthermore, modern mobile phones are also able to cope with the separation of interference from speech.
In the experiments carried out by our team, it became apparent that the skimmer copes when there is, so-called, visibility between the ultrasound emitter and the microphone. If there is a solid obstacle in the path of the sound, the jamming effectiveness drops to zero. It is enough for the voice recorder to be placed in the back pocket of the trousers for a jammer aimed at us from the front to be completely ineffective.
Our effectiveness rating is 3/10, and taking into account the possible damage to hearing due to being in a room with 105 – 110 dB of noise, we advise against the use of ultrasonic jammers.
Securing the room against external surveillance
Although laser microphones are generally unlikely to be used, the risk is real for certain individuals. In order to protect the room from the possibility of external eavesdropping, whether using earlier generations of laser microphones or seismic microphones, it is necessary to install vibro-acoustic systems. The placement of a sufficient number of heads should drown out external eavesdropping. Solutions of this type are recommended as a complement to comprehensive multi-element solutions. As a component of a larger security system, we rate the effectiveness at 9/10.
Audible wiretap jamming systems
Audible jamming is similar in operation to ultrasonic jamming, although, when used correctly, its effectiveness is significantly higher than that of a humming device. We tested the DRUID D-06 solution, which consists of a head unit and 4 sets of headphones with microphone.
In order to secure a Druid conversation, all participants must wear the aforementioned headsets plugged into the main unit. When switched on, the unit generates audible noise, which is adjusted in real time according to the users’ spoken words. Druid filters out the noise, so that in the headsets, the speakers hear clear sound. For eavesdroppers placed in a room, the entire conversation is ‘covered’ by a variety of sounds that are virtually impossible to filter out during post-processing of the recordings.
The downside of this solution is the need to use headsets and the noise audible to people in close surroundings, such as adjacent rooms. The system is sensitive to errors associated with the use of headsets – when the microphone is away from the speaker’s mouth, the effectiveness of jamming decreases significantly. The reason for this is that the masking sound is generated to the input signal from the microphone. If the microphone away from the mouth picks up quieter sound, the generator will also generate quieter sound and this is regardless of the actual volume of the speech. Our rating is 7/10.
Summary
Due to the variety of eavesdroppers in use and something as mundane as the laws of physics, it is not easy, effectively, to jam an eavesdropper. Each solution has its limitations, which make the level of assurance unsatisfactory. Is it worth spending money on safeguards whose use may do nothing? In our opinion, no, although ultimately the risk assessment remains with the user of said jammers. Note that a false sense of security can lead to immeasurably greater losses due to the leakage of sensitive information.
By far the highest level of security can be achieved by combining cyclic eavesdropping detection with room security with a vibro-acoustic system and a DRUID D-06 type acoustic jammer. Procedures restricting the possibility of bringing electronic equipment into the premises will further seal the security.
