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ZAP Checker
Field strength indicator and bug detector

ZAP Checker is an sensitive field strength indicator that detects and displays electromagnetic RF signals over a wide frequency range, developed around 2002 by Alan Susals of Alan Broadband Co. in Fair Oaks (California, USA). Several upgraded models were introduced over the years.

The device responds to nearly any type of RF signal in its vicinity, and has an adjustable sensitivity. Furthermore, its analogue meter scale can be switched from logarithmic to linear, making it extremely useful for bug finding.

Apart from the large and clear analogue meter, its provides a visual indication by means of two LEDs, a red one and a green one, plus a vibrator that can be switch on when needed. The image on the right shows the initial basic model 180 which features a 10 MHz to 4.5 GHz frequency range. The unit is housed in an ergonomic case.
ZAP checker

Later models had an extended frequency range and also provided an acoustic feedback, allowing the nature of particular signals to be identified more easily. In addition, some of the later models featured a socket for connection of an external (directional) antenna, such as a log-periodic one. Unfortunately, ZAP Checkers are no longer in production as the manufacturer, Alan Broadband, went out of business around 2012. They are sometimes being offered on auction sites like eBay.

The device is only suitable for finding narrowband continuous wave (CW) transmitters and wide­band burst-type transmitters, such as WiFi base stations and GSM phones. The presence of such signals in a room is easily detectable and the device is quickly found. It is not suitable for finding pulse-based bugs, such as the CIA's SRT-56 transmitter, due to the extremely low energy density of its 350 MHz signal. Even when held against the antenna, ZAP produces no reading whatsoever.

ZAP checker Front view ZAP Checker Interior Direct bonded chip?
The ZAP Checker has very few controls and is extremely easy to use. Yet it provides a quick and reliable way to check for the presence of RF signals. The device is switched ON by turning the rotary knob away from the zero-position. The same knob is used to adjust the sensitivity (30dB). Once switched ON, the analogue meter shows the current signal level, assisted by two LEDs (a red one and a green one) that provide a very useful feedback when operating the device in the dark.

A slide switch to the left of the sensitivity knob, is used to select between a logarithmic and a linear response of the meter, whilst another slide switch, to the right of the meter, can be used to turn on the internal vibrator, which can be useful for concealed operation. It provides a physical feedback, that consists of a intermittent vibration that is proportional to the signal strength.

The case of of the ZAP Checker can be opened by removing two small screws from the battery compartment and separating the two plastic case shells. This can be a bit tricky as there are three notches that hold the two case halves together.

The image on the right shows the PCB, which is mounted to the rear of the analogue meter. The big coil at the center is a non-resonant helical antenna. At first sight ZAP may seem a simple device, but the real beauty is hidden under a black epoxy blob just behind the antenna...

  • 180
    10 MHz - 4.5 GHz
  • 185
    3 MHz - 5 GHz
  • 190B
    1 MHz - 8 GHz
  • 300
    1 MHz - 8 GHz with socket for external antenna
  • 126
    1 MHz - 14 GHz
  • 270
    Yellow with directional antenna
  • Frequency
    10 MHz - 4.5 GHz
  • Length
    128 mm
  • Width
    55 mm
  • Weight
    132 grams (including batteries)
  • Antenna
  • Sensitivity
    100µV (at the lower frequencies)
  • Batteries
    2 x 1.5V AA-size, 80 hours life (50 hours when vibrator is on)
  1. Bob Grove (W8JHD), Zap Checker 270
    Monitoring Times (magazine), June 2005.

  2. ZC 185 ZAP Checker
    YouTube user Edmk2009. 17 October 2011.
Further information
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Crypto Museum. Created: Sunday 21 May 2017. Last changed: Sunday, 21 May 2017 - 16:49 CET.
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