Surveillance - Straight Talk

Alan Broadband Company

When faced with the challenge of finding a covert device, there are dozens of counter-surveillance products to choose from to help with the quest. The plethora of these products is mind-boggling.

Many boast unsubstantiated claims and non-standardized specifications - making it hard for even the professional to choose from among them. It is no wonder the uninitiated security person is confused and misled by the hype associated with all these counter-surveillance instruments.

It is possible to identify a few critical characteristics of outstanding detection devices. Identifying these characteristics and discussing them in understandable terms will help the security person to cut through the chaff of confusing product hype.

When discovering transmitting covert devices (such as camera and audio bugs), we are dealing with detecting and pin-pointing signals from those devices. We are basically dealing with a receiving instrument. Like a receiver, these counter-surveillance instruments must excel in providing:

  1. High sensitivity – to sense covert devices from a distance.

  2. A broad receiving bandwidth – that covers the frequencies of the covert transmitters.

  3. Different modes of detection – that enable us to initially detect the miniscule signals from far-off transmitters and then home in and pinpoint their locations.

  4. Display Modalities – which allow us to see measure RF signals or detect them in an unobserved manner, even at night time.

  5. Portability and ease of use – to free us from the burden of lugging around heavy, cumbersome equipment.

  6. Reasonable economy – enabling detection personnel to purchase and operate the instruments at an affordable price.

The above requirements are a tall order. Previously, it was not possible to produce such devices. However, now, we have newer instruments built with micro miniaturized circuits that enable us to realize these requirements. That fact is the basis for eliminating the great majority of current counter-surveillance instruments from the list of preferred products.

ZC Model 180ZC Model 180

The current products were made with an older generation of technology. For example, they almost universally use some kind of diode-detection scheme – that is akin to using a crystal-diode detector for the receiver (a crystal-radio).

Newer instruments employ several stages of signal amplification before active detection – overcoming the limitations of diode detection and making them truly hundreds of times more sensitive than the older units. These new detection circuits also work much better at the higher frequencies and provide enhanced broadband capabilities.

Generally the older apparatus uses higher voltage batteries to run the older-generation electronic circuits. It is common for these later-generation devices to run on 9 volt or 12-volt batteries, or a stack of 5 to 10 dry cells or Nicad batteries. The newer devices run on miniature chips that go into the latest portable cell phones, PDA’s, wireless devices and GPS receivers – often running nicely on only 3 volts (2 cells).

The changes that have occurred over time in television sets, monitors, computers, digital cameras, etc., have now also occurred in counter-surveillance instrumentation. For higher performance, greater ruggedness and reliability, vastly improved portability – and often a lower price we can turn to the newer generation of electronic apparatus.

Inside Model 180Inside Model 180

Sensitivity – How does sensitivity affect the operation of counter surveillance apparatus? In covert detection, sensitivity is the name of the game! We must be able to detect the tiny signals that are transmitted from a covert device at a distance; the better the sensitivity the farther the detection range.

With previous equipment one literally had to “sweep” all the walls, floor and ceiling from 1 to 3 feet distance in order to detect weak signals from the bug. That is long, hard, exacting work!

With the newer counter-surveillance instrumentation, the sensitivity is hundreds of times greater than the older units.

That corresponds to detecting covert transmitters from 12 to 25 feet away – making it easier and more effective to detect these devices – for example from the door of the room. This changes the nature and necessity of those rigorous, older "sweeps”.

The newer counter surveillance instrumentation will detect and measure small signals down to the ambient, baseline levels of radio-frequency radiation. Local baseline levels are often due to the local FM and TV broadcasts in the area. Any signal that exceeds that baseline level will be detected.

To give one a basis for comparison with older detection equipment, the newer instrumentation will detect operating “sealed” microwave ovens (2.4 GHz frequency) at a distance of 30 to 60 feet as compared to 1 to 6 feet with the older equipment. If you want to detect 2.4 GHz covert transmitters (a favored frequency for bugs), it is more effective and time-efficient, to do so with the newer apparatus.

Broad Bandwidth. A professional counter-surveillance person will often use expensive, heavy, specialized equipment such as spectrum analyzer, frequency counters and tunable receivers to tune-in on covert devices. The general security person is often more interested in detecting the transmitting device within a broad band of frequencies.

The exact frequency is not known or even needed in most cases. A large band of frequencies are checked and any covert device within that spectrum is detected. The newer counter-surveillance instrumentation spans a 10MHz to 4.5 GHz bandwidth with particularly high sensitivity at the higher frequencies. This means that common frequencies used for covert devices (3.5, 2.4, 1.8, 1.2 and 0.9 GHz, 450, 140, 100 MHz and below to 72, 49 and 27 MHz) are all detected with the newer apparatus.

That decreases the chance of missing the covert device by not tuning into the proper frequency or not having enough sensitivity to detect the device at its operating frequency. Moreover, it doesn’t matter if frequency – hopping, spread spectrum, trunking or random bursts over broad frequencies are used – they will all be equally detected with the newer instrumentation.

Model 270 with Optional AntennaModel 270 with Optional Antenna

Detection Mode – The newer apparatus has both LINEAR and LOGARITHMIC detection. In the linear mode the weakest 10dB of signals are detected and displayed fully on an analog meter and LED displays. This is the mode to use for initially detecting the presence of a covert transmitter from a distance.

The sensitivity of the newer instrumentation is controllable by a variable attenuator (sensitivity control). As the detected covert device is approached, and its detected signal level becomes stronger, the variable attenuator is adjusted to keep the measurement on the meter scale.

In the close vicinity of a transmitting device (4-8 feet from a 10 milliwatt transmitter), the meter will be at full scale. Then, by switching to the logarithmic mode, the meter reading is reset to a lower level. In the LOG mode the scale reading of the newer instrumentation spans a 60dB, 1000 to 1 range of signal strengths.

The relatively low signal level in the LOG mode will increase in a controlled manner as the covert device is approached. Even though the detecting instrument is brought within a few inches of the bug (a close proximity that normally would swamp the detector), it is adjustable to give a valid reading in the LOG mode. In this manner the covert device is detected in a pinpoint fashion.

Wide dynamic-range LOG detection is available on the newer counter-surveillance instrumentation as well as on sophisticated, costly, older apparatus. An intermediate detection range (combining elements of linear and partial logarithmic detection) is utilized on the newer instrumentation to sort through multiple signals of varying strength from different signal sources.


An analog signal meter is used as the primary display for the newer apparatus. Yes, an analog meter is an older type of display; however, it provides a quicker, more readable, quantitative indication of the signal levels. Do you prefer an analog or digital watch? A digital readout would constantly be changing numbers in rapid succession. An LED bar-graft display does not present the display measurement as precisely and quantitatively as an analog meter.


Optional Log Periodic Antenna

The newer instruments also employ green and red LEDs to give secondary display information from a distance or at nighttime. The lighting of the colored LEDs corresponds to the signal levels seen on the analog meter. At a zero or a low signal level the green LED is fully lit and the red LED is off. As the signal reading increases the green LED gets progressively dimmer and the red LED begins to be illuminated.

At a middle signal level both colored LEDs are moderately lit. At the highest signal level, the red LED is brightly illuminated with the green LED being fully extinguished. This scheme allows the newer instrument to be placed at a distance (beyond the view of the analog meter), yet still to provide a valid indication of the signal strength. (The newer instrumentation can be stood upright to view these measurements).

The LEDs respond quickly to signal changes as compared to the inertial lag of the analog meter needle. When detecting digital signals (which switch on and off rapidly) the LEDs give a quickly alternating illuminated display. This is a means for distinguishing digital transmissions.

The newer instruments are miniaturized to allow them to slip into a pocket or purse. They also contain a switch enabled silent vibrator mode. By using the silent vibrate mode in a pocket or purse the operator can detect transmissions from covet devices without being observed to be making these measurements.

One can still detect the presence of covert transmitters discreetly while attending a meeting – or meeting a contact person in an open field. The newer apparatus enhances the usual vibration-detection feature by modulating the vibration amplitude depending upon the detected signal strength. An operator can use the newer instrumentation to not only detect covert transmissions in a discrete manner, but can also determine the source of the transmissions by noting the increased vibrations as the covert device is approached.

Small and Portable

The newer instruments are small, portable and lightweight. This is possible by using miniaturized circuitry, only requiring 2 AA batteries (3 volts), and encasing them in rugged, customized polycarbonate cases. These newer instruments also contain 2 fixed, internal antennas (one for higher frequencies, the other for lower frequencies), which do not protrude from the inside of the case. These internal antennas detect signals in a consistent, repeatable manner since they do not need to be extended or adjusted in any way.

Reasonable Economy

The newer instruments are presently available in 2 models. Model 270 Zap Checker contains all the attributes noted above and has an additional switched coaxial antenna input. It sells for $269.00 alone or $329.00 with an optional 2.4 – 6.4 GHz LOG PERIODIC antenna. Model 270 weighs 5 oz. with batteries installed and will operate for 50-60 hours using 2 AA alkaline batteries.


2.4 GHz Loop Yagi Antenna

Model 180 Zap Checker also contains the characteristics described above but does not have a switched antenna input. It sells for $89.00; weighs less than 5 oz. with batteries installed and will operate for approximately 80 hours using 2AA alkaline batteries.

There is a big price difference between the Model 270 and 180. Is the switched coaxial antenna input the only difference? No, there are several differences between the models. Model 270 has a different printed circuit board and uses a higher frequency pre-amplifier, has different internal antennas, has a broader variable attenuator (sensitivity control), and can be switched between LOG, LINEAR, and MID range detection modes. The primary difference is the ability to switch between the internal antennas and an external SMA coaxial input using isolated mechanical/electronic switching.

The coaxial input connector of the Model 270 enables it to be used with directional, frequency-specific antennas; high pass, low pass and band pass filters, and different external attenuators. This changes the nature of portable counter-surveillance equipment – from solely omni directional receiving equipment to frequency selective, Radio Direction Finding (RDF) apparatus. The more directive and frequency specific the antenna, the more directionally sensitive and bandwidth limited the ZC 270 becomes.

The ZC 270 is available with a 2.4 to 6.4 GHz LOG PERIODIC antenna as an option. This accessory increases the sensitivity by about 3 times within the 2.4 – 4.5 GHz detection range of the ZC 270/antenna combination. Sensitivity along a specific direction for 2.4 GHz can be increased 4 to 8 times by using longer antennas such as the Models 1209LY, 1215 LYRM and 1221 LYRM Loop Yagi antennas available from Directive Systems, 177 Dixon Road, Lebanon, ME. 04027 U.S.A., (Ask for the SMA connector for the ZC Model 270.)

The Zap Checker Model 270 with the optional LOG-PERIODIC antenna sells for U.S. $329.00. Without the antenna it is priced at $269.00. The Zap Checker Model 180 sells for U.S. $89.00. For shipping and handling add $7.00 in the U.S.A. or $13.00 to UK/Europe for either model. Send orders or inquiries to Alan Broadband Co., 93 Arch St., Redwood City, CA 94062, U.S.A. Tel. (650) 369-9627; Fax (650) 369-3788,, [email protected]

To view our article 'Counter Surveillance Detection - A Primer' please click here and to view 'Counter Surveillance Detection - A Second Look' please click here.

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