The Mini Monitor 900 Series of Geiger Counters and Ratemeters, manufactured in the UK by Mini Instruments Ltd (and latterly, Thermo Scientific) are amongst the most highly-respected radiation measurement and monitoring instruments in use today.

Over the years they have earned a good reputation for reliability, performance, versatility, ease of use and value for money. Mini Monitor 900s continue to be a popular choice in teaching, research, hospitals, industry and amongst environmentalists and enthusiasts. Here’s just a brief outline of the main features:
  • Large, logarithmic meter, accurately displays both very low and high levels

  • Portable & bench operation (mains adaptor or 6 x AA cells)
  • Battery life 300 hrs (typical, 4 hrs use per day)
  • Ease of use – single control for battery check, power on & audio mute
  • User-settable threshold alarm

  • Battery check
  • Built-in sounder with Mute function
  • Probe cradle and carry handle
  • External DC power & charge socket  
  • Rugged all-metal case
  • Curly probe lead
  • Available with a range of probes
The Mini Instrument 900s that we stock were all previously owned but they have generally been very well maintained regularly calibrated and are in good working order. In addition to any necessary case refurbishments we carry out a full range of operational checks, including probe supply testing & adjustment and pulse-calibration, which we repeat immediately prior to despatch. All models come with a 6-months guarantee.

Please note that these instruments may have been in use for several years so there can be some light scuff-marks and minor scratches, but unless stated otherwise they are full working order with an up to date pulse calibration check. Unfortunately we do not have any manuals for these models and they are supplied without any accessories, other than battery holders. We grade the cosmetic condition of the instruments that we sell from A to D, with A+ indicating ‘almost as-new’, and D- ‘tatty with noticeable scratches, etc.


CURRENT STOCK (see photos, actual products, more available on request)
Mini Monitor Type 900/E (MFG001)
Probe: type E thin mica end window GM tube 6.0cm² cable
Meter Scale: 0 – 2k cps
Condition A
Price £375.00, inc. UK shipping
Thermo Scientific 900/42B (MFG015)
Probe type 900/42B scintillation probe, TNC connector
Meter Scale: 0 – 5k cps
Cosmetic Condition A+
Price: £600.00, inc. UK shipping

Mini Monitor Type 900/E (MFG001)
Probe: type E thin mica end window GM tube 6.0cm²
Meter Scale 0 – 2k cps
Cosmetic Condition B
Price: £350.00, inc. UK shipping

Thermo Scientific 900/E (MFG001)
Probe: type E thin mica end window GM tube 6.0cm²
Meter Scale 0 – 2k cps
Cosmetic Condition A
Price: £375.00, inc. UK shipping

Mini Monitor 900/MC20
Probe: Type MC20 Compensated GM tube, TNC connector
Meter Scale: 0 – 75 uSv/hr
Cosmetic Condition A-
Price: £425.00, inc. UK shipping

Mini Monitor 900/44A (MFG016)
Probe type 900/44A scintillation probe, TNC connector
Meter Scale 0 – 5k cps
Cosmetic Condition A-
Price: £650.00, inc. UK shipping

New Buyers Please Click HERE

N.B. Prices shown include UK shipping

Very Important Stuff For Overseas Buyers:

The prices shown are for UK buyers and include insured courier shipping. Non-UK buyers: due to the weight variations of  these instruments, please email us at  or click the Contact Us link at the bottom of the this page for up to date shipping costs. Please also note that this item may be prohibited or restricted in some countries.


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Mini Monitor 900s Geiger Counters & Ratemeters - Prices start at £350.00

  • Product Code: Mini Instruments 900
  • Availability: In Stock
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