Independent comparisons. We may earn from shop links. More info

How to use a geiger counter

Updated: October 2026

The number jumps when you have not moved, and it is easy to treat that as a dose or a safety verdict. Learning how to use a geiger counter means taking a background in the same room and comparing an object in counts, not against a borrowed safe microsievert figure. Model choice stays on the [Geiger counter comparison](/hub/measuring-equipment/geiger-counter). Peter F. updated this guide on 16 October 2026 from UKHSA and BBC Bitesize. A qualifying purchase can earn us a commission at no extra cost to you. Radon is most of average UK exposure and these tubes do not report it in Bq/m³. The [geiger counter radon](/hub/measuring-equipment/geiger-counter/sub/geiger-counter-radon) page is that test.

The number jumps when you have not moved, and it is easy to treat that as a dose or a safety verdict.

Our top picks

GQ GQ GMC-800

Best overall

GQ GQ GMC-800
8.6/10about £80.98
View offer
FNIRSI FNIRSI GC-01

Alternative

FNIRSI FNIRSI GC-01
8.2/10about £50.79
View offer
Soogua Soogua Geiger counter

Preis-Tipp

Soogua Soogua Geiger counter
7.6/10about £37.60
View offer
On this page
  1. 1.What the number on the screen is
  2. 2.Take a background in the same room
  3. 3.Compare an object without fooling yourself
  4. 4.When the meter is the problem

What the number on the screen is

A click is a count. The tube has registered an ionising event. It has not measured the energy, and it has not named an isotope. Counts per minute are the unit for higher than the table. Microsieverts per hour are the maker's conversion, usually for gamma, and they mislead you on a beta source. UKHSA's figure of about 2.6 mSv a year, of which radon and thoron are about 1.1 mSv, is an average exposure. Do not divide it into a target for your GC-01 or GMC-800. The display wanders because decay is random.

Take a background in the same room

Charge the meter before you trust a low number. Soogua reviews say it arrived uncharged and would not start from a laptop USB-C PD charger, while the included cable did. The GMC-320S needs a long USB charge, and a short press looks like a fault because it stays on only if you hold the power button. Switch on, step away from the object, and hold the meter off your body. Stay still for several minutes. Write the CPM, the µSv/h if shown, the time, and what was nearby. Repeat the blank once. If the two readings sit in the same neighbourhood, that is the background for that room today. If they do not, count longer. Your blank is the comparator. The geiger counter buying guide explains why a listing's dose span, if it has one, is not that comparator.
GQ GQ GMC-800

Testsieger

GQ GQ GMC-800
8.6/10about £80.98
View offer

Compare an object without fooling yourself

Use the same face at a distance you can repeat tomorrow. A few centimetres, or a turn of the case, will move a beta response more than the object did. Write CPM first. If µSv/h rose and CPM did not, distrust the dose figure. If both rose clearly above the two blanks, you have a higher count than the table, not a certificate that the object is safe or unsafe. A banana, granite, or uranium glass can click. That click is not a food-safety result and not a reason to rip out a worktop. On the FD-5000, reviewers often see a strong response only on the test card, around 27 µSv/h or about 35 µSv/h. The best geiger counter page ties each listing to a job. This routine does not rank them.

When the meter is the problem

Silence is often the meter, not a safe room. A UK GC-01 review says the stock unit has no click until the firmware is changed, and others describe a red light after a few days or no response to charging. A Soogua alarm stuck until the battery was disconnected. Charge with the expected cable, hold the power button if the screen only flashes, and only then decide the room is quiet. A meter that cannot finish a background is not evidence of a low dose. Stop and get help when a reading stays far above a fresh background and you cannot account for it, when you think you have found a source, or when the place may fall under IRR17. Move away. Contact UKHSA or the local authority. Call 999 in an emergency. Do not open a smoke alarm.

Common questions

What should I do before I measure an object?
Charge the meter, take two blank readings of several minutes away from the object, and write the CPM. Hold the GMC-320S power button or it looks dead. Use the cable that actually charges a Soogua if a laptop port does not. Those blanks are the only baseline this method uses. A published CPM example is not your result.
Why does the number move when nothing has changed?
Decay is random, so a short count wanders. BBC Bitesize uses about 18 CPM as a teaching example, not a home limit. The US NRC's range of about 5 to 60 CPM also depends on place and tube. Count for longer, repeat the blank, and compare averages. A jump of a few CPM is not a new source.
Should I trust µSv/h or CPM?
Trust CPM against your own background. Treat µSv/h as the maker's gamma estimate. Do not convert 2.6 mSv a year into a target on the screen. The GC-01 maker page conflicts on dose rate, and this GMC-800 amazon file does not print the PDF's 0.00 to 2,000 µSv/h. If the units disagree, write both and lean on CPM.
How close do I hold it?
Close enough to repeat, and the same distance on a second pass. A few centimetres matter for beta, and these cased meters are weak on beta through the shell. Do not open the case. Note the face you used. Reviewers say the GMC-800 sensor is on the side, so rotating the meter changes the count.
The meter is silent. Is that a low dose?
Often it is a fault. GC-01 reviews include no click until firmware is changed, and units that died within days. The GMC-320S must be held to power on. A Soogua may arrive flat, and one alarm stuck until the battery was disconnected. Charge it and hold the button. A silent faulty meter is not a low dose.
When do I stop and call someone?
Stop if the count stays far above a fresh background, if you have found a source, or if the place is a workplace. Move away and contact UKHSA or the local authority, and call 999 in an emergency. Do not open a smoke alarm or a test card. After hospital treatment, follow the clinic. The meter is not a clearance certificate.

Related pages

GQ GMC-800 vs FNIRSI GC-01

Geiger counter

Best geiger counter: log, value pick, and who should skip

Geiger counter buying guide: tube, units and limits

Geiger counter radon test: CPM is not the house result

Sources

UKHSA, Public Health Wales, the Health and Safety Executive and the Ionising Radiations Regulations 2017, plus manufacturer pages and the amazon.co.uk listings read on 16 October 2026. Prices move. Nothing was laboratory tested or UKAS calibrated.

  1. UKHSA, UK ionising radiation exposure, June 2025 (retrieved 16 October 2026)
  2. UKHSA, radon Action Level and Target Level (retrieved 16 October 2026)
  3. UKHSA, measuring radon (retrieved 16 October 2026)
  4. Public Health Wales, radon (retrieved 16 October 2026)
  5. HSE, ionising radiation legal base (retrieved 16 October 2026)
  6. Ionising Radiations Regulations 2017, Schedule 3 (retrieved 16 October 2026)
  7. GQ Electronics, GMC-800 user guide (retrieved 16 October 2026)
  8. FNIRSI GC-01 product page (retrieved 16 October 2026)