FNIRSI offers a wide range of tools, including oscilloscopes, multimeters, soldering irons, and various measurement devices. In this review, we take a look at the second version of their Nuclear Radiation Detector (or Geiger counter), the GC-02.
 
 
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Nice design for this meter, with USB-C port for battery charging.

Overview

The FNIRSI GC-02 is a newly launched nuclear radiation detector (also known as a Geiger counter) featuring a sleek design and a compact size. It uses a Geiger-Müller tube to detect ionizing radiation, including gamma rays, beta rays, and X-rays. The device is equipped with a 1.5-inch IPS high-definition LCD that offers a clear and well-organized interface, displaying real-time values, average values, maximum values, and cumulative readings at a glance. Users can configure alarm thresholds, adjust sleep and shutdown times, and switch between eight languages. Additional features include a timed monitoring mode and a history view that records up to 10 measurements in a non volatile memory, which are preserved when the device is powered off. The GC-02 is powered by a rechargeable Lithium battery.

Specifications

The specifications provided by FNIRSI are as follows:
  • Size: 106.5 × 44.5 × 25 mm
  • Detector: Geiger-Müller tube
  • Detected Radiation Types: Gamma rays, beta rays, X-rays
  • Dose Current Rate: 0.00–1000 μSv/h (1 mSv/h)
  • Cumulative Dose Equivalent: 0.00 μSv–500.0 mSv
  • Energy Range: 48 keV–15 MeV ≤ ±30% (for Cs-137)
  • Sensitivity: 80 CPM/μSv (for Co-60)
  • Dosage Units: μSv/h, μGy/h, mR/h, CPS, CPM
  • Battery Capacity: 850 mAh
  • Alarm Method: Light, sound

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Getting Started with the GC-02

 
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Included accessories.

Inside the cardboard box, you’ll find the Geiger counter itself, a USB-C charging cable, a short strap, and a printed manual. Upon first powering it on, you are prompted to select a language from eight options: Chinese, English, Russian, German, Japanese, Portuguese, Spanish, and Korean. Unfortunately, French is not available. However, the device is simple enough to use that this shouldn't pose much of an issue for French customers. Once the language is set, the main screen is displayed.
 
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Main view.

The main screen displays the real-time radiation intensity. In the upper left corner, the device’s operating time is indicated, while the upper right corner features an icon showing whether the buzzer is activated. The buzzer volume can be adjusted in the settings, including a fully silent mode; that icon provides a quick reference to its status. The battery level is also displayed in the top right corner.

In the central part of the screen, below the real-time value, a thin white horizontal strip shows the total absorbed dose recorded since the device was turned on. This value represents the integration of instantaneous doses over the total operating time. At the bottom of the screen, the current alarm thresholds are displayed: on the left, the dose rate in microsieverts per hour, and on the right, the cumulative dose alarm threshold. Additionally, a red LED on the front of the device flashes each time a particle is detected by the Geiger tube.

To navigate to other screens, press the left or right buttons at the bottom of the device. The next screen features a scrolling graph similar to an oscilloscope with a very low sweep frequency, allowing users to observe radiation level fluctuations. Average and maximum measured values are displayed at the bottom.
 
 
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Graph mode.

The next screen allows users to perform timed measurements. After setting a start time and a stop time, the device automatically records radiation level during the configured time period. Once monitoring starts, the screen interface changes: the lower part lights up in vivid colors, and the time counter above the dose rate starts counting. The instrument records cumulative, average, and maximum values in a cycle. When the stop time is reached, the interface changes again, stopping the counter and graying out the recorded values.
 
 
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Recording mode, with ongoing measurement on the right. Notice the slightly different colors.

After completing such a measurement, results are stored in memory. These results can be accessed on the next screen, organized in blocks: Measurement 1 (M1), M2, etc., with up to 10 measurements retained. The most recent measurement is assigned the highest number and appears at the top. These measurements are stored in non-volatile memory and remain accessible even after powering off the device.
 
 
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List of measurements, here with only one recording.

When a new measurement is recorded beyond the 10-entry limit, the oldest entry is deleted. There appears to be no way to manually delete stored measurements except by performing a factory reset.

Settings

Holding down the settings button on the right side enters the settings menu, which takes a few minutes to get used to. Initially, it appears to have only four icons: Alarms, Alarm Values, Sleep Settings, and General Settings.
 
 
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The Settings page.

However, there are sub-menus within these categories. Select a category by pressing OK (be careful — holding OK for too long turns off the device), then use the left and right buttons to browse available settings. The main options are enabling or disabling alarms, adjusting alarm thresholds, changing measurement units, configuring sleep and shutdown times and adjusting screen brightness.

Practical Applications for the GC-02

Owning a Geiger counter like the GC-02 provides peace of mind by detecting radiation levels in everyday environments. Some homebuyers or landowners like to check for potential radioactive contamination left by previous occupants. Hobbyists and researchers use it to explore naturally occurring radioactive materials such as granite.

Geiger counters are also useful for checking vintage items for radioactivity, which can even become a fun hobby! For example, in the past old watches and instrument dials were painted with radium-based paint to make them glow in the dark. Fortunately, other luminous substances are used instead nowadays. Some decorative and kitchenware items, such as uranium glass or pre-1969 Fiesta-Ware, may also be radioactive. Carrying a compact Geiger counter can lead to interesting discoveries at flea markets!
 
 
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Testing various items looking for radioactivity.

This vintage military compass looks great with its radioactive logo, indicating the presence of a tiny Gaseous Tritium Light Source (GTLS). However, its beta radiation is so weak that only a scintillation counter could detect it — no surprise that the GC-02 doesn't register it. On the other hand, this old camping lantern mantle contains thorium, which emits significantly stronger radiation and is easily detected by the GC-02.
 
 
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Internal construction of the GC-02.

Internally, the GC-02 has a simple and clean design. Its PCB features a CH32F203 microcontroller from WCH and a Geiger tube, accompanied by a piezo buzzer and a lithium battery.

If you're looking for a compact Geiger counter housed in a sleek and elegant casing, the FNIRSI GC-02 is worth considering.