Electronic Surveillance Threats

♦ Electronic surveillance threats – defending a facility against electronic surveillance is a serious challenge and one that hasn’t been made any easier by the proliferation of computer networks and wireless. Not only are businesses under threat from phone tapping, and video and audio surveillance, wired and wireless computer networks offer attackers a new dimension of intrusion.

Even the simplest electronic surveillance devices are diverse, with room transmitters being among the most common. Their role is to detect all the environmental noise emanating from the location in which they’re planted.

Primary variations with room transmitters relate to differences in power sources. In this case, either battery or mains power and it’s the battery powered devices that are most diverse. Such devices can be secreted inside almost any object allowing for their minimal space requirements. Examples include the inside of pens, calculators, clocks, photo frames, under carpet, behind curtains and underneath or inside furniture.

The types of battery used to power these devices varies too, depending on the design, size and planned use of the device. Self-contained transmitters designed for surreptitious surveillance favour small button batteries or higher performance hearing aid batteries. When size is less of a concern and length of transmission a higher priority, larger and longer lasting batteries can be used, including the latest lithium types.

Average transmission devices typically have dimensions around 19mm x 12mm x 9mm. Should a small transmitter be built into a pen or a calculator, transmission range will be limited, around 15-20m, though the use of lithium batteries will increase the range.

Mains-powered room transmitters draw current either directly from the mains voltage or trickle charge a battery that’s also used to power the device. The advantages of this technique where electronic intruders are concerned include the fact there will be less impact on main power sources that could be monitored for fluctuations. Should mains power be lost the device will continue to operate.

The key technical issue for mains powered transmitters is to reduce 240V of alternating current to a direct current, low voltage output of 6-18V. Designers are required to combine transmission circuitry along with a voltage dropper, rectification, smoothing and voltage stabilization circuits.

As a rule, the most popular way to get the small current and voltage requirements is to use a high voltage capacitor to act as resistance at the 50/60Hz mains supply frequency. Low power can be partially offset by injecting some radio power into the mains.

Should there be enough room and a sufficiently low risk of detection, it’s sometimes possible for a stepdown transformer to be used – this is inherently more reliable that capacitor leakage or dropper resistance techniques. It’s also possible for a transformer to supply a far greater level of power to a strong transmitter.

AC units can be located inside walls, ceilings, under floors, inside office equipment, in mains-powered clocks and within lamps and lamp holders to name just a few possibilities. One of the favoured methods of installing an AC bug is to simply plug in a dummy double adaptor to a power point in the room you wish monitor. Despite the simplicity of this technique, only the most observant would notice and even then, would be most unlikely to consider the appearance of the unit a threat to security.

Electronic intruders wishing to secure a standalone mains-powered transmitter are usually supplied with a square plastic box about 50mm x 50mm x 18mm, or an encapsulating board. There will be a pair of trailing leads coming from these units for connection to the live and neutral lines of domestic AC.

There are still PSTN telephone transmitters. These are connected to target telephone systems and transmit information to a receiving station located nearby. The 2 basic models are the series-connected transmitter and the parallel-connected transmitter. Both types either draw their operating voltage from the PSTN phone line itself, or carry their own batteries that may be trickle-charged from the phone line.

Series connected transmitters are connected between a telephone socket and a telephone. In this configuration, only that extension will be accessed by the listener. But in the event a series transmitter is used and located on the incoming wires of a 2-pair cable on the other side of a telephone socket, all extensions of the line can be accessed.

Muliplex telephone systems make life extremely hard for electronic intruders trying to record communications. Because these systems multiplex more than one signal onto a 2-pair cable, an intruder would need to employ a de-multiplexer to access phones.

Partially connected transmitters are different. Both incoming feed wires are connected to the parallel connected device, and this means the information will be transmitted if either phone is used. With a series device, the wiring of the telephone must be disconnected to allow insertion of the transmitter. But installation doesn’t mean cutting and stripping of feed wires. Instead, the device can be installed in a junction box that offers sufficient room, or even in a telephone.

Series devices are easiest for security managers to detect using one of the counter surveillance devices on the market that alert security staff to temporary disconnection of phone lines. It’s possible for alarm panels monitoring alarm systems to also monitor phone lines for integrity, with any breaches then reported.

Parallel series devices, however, can be installed without temporary line breaks and without effect on resistance. This makes them harder to detect, though if the unit is drawing power from its host, this will cause a voltage drop. Parallel devices are often equipped with alligator clips requiring no more than a few millimetres of cable to be stripped or a pair of bare terminals.

Battery-powered types are harder to detect and more effective in their operation. With their greater operating current, they can achieve greater operating ranges than bugs, giving 500-1000m ranges instead of 25-50m. Even harder to detect are small rain-proof telephone transmitters that can be connected to any point of the exterior wiring as it leaves a building or joins a telephone pole. Such a device might never be detected.

Mobile phones are usually tapped using spyware. This is a whole other science – it’s possible for experts to search for spyware and users might notice quirks like rapid battery drain, though it can be difficult to know whether this is caused by an illicit piece of software, too many open apps, or simply an aging battery.

There are 2 primary groups of microphones available to an individual or organization seeking illicit access to communications. These are omnidirectional and unidirectional. Unidirectional microphones are portable and can be aimed at a target. They’re a parabolic dish-mount device that can be hand-held or tripod mounted. Such units offer excellent results for the electronic intruder. Using a 45cm reflector, high quality sound can be obtained at 250m. This performance increases fourfold if the reflector size is doubled but the unit becomes much more visible.

Omnidirectional units pick up audio signals coming from any point of the compass and in surveillance devices they usually have a diameter of about 6mm. As a rule, these devices will be more effective towards the front. Another type of microphone, the spike mike, is mounted on the end of a spike or probe. Microphones can be connected to the audio input of a miniature transmitter, allowing remote monitoring of conversations.

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