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Radiation Alert MONITOR4 Analog-Based Ionizing Radiation Detector
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Radiation Alert MONITOR4 Analog-Based Ionizing Radiation Detector

By Radiation Alert
4.1 out of 5 stars  See all reviews (15 customer reviews)

List Price: $350.00
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Specifications for this item

Number of Items
Material Type
Part Number
Temperature Range
neg 4/131  Degrees Fahrenheit
Brand Name
Radiation Alert
Import Designation
Made in USA

Product Features

  • Radiation detector used to check levels of potentially harmful ionizing particles and rays in the environment and in objects such as particle accelerators, x-ray shielding, and industrial gauges
  • Detects ionizing radiation types such as alpha and beta particles, and gamma rays and x-rays
  • Dual-scale analog meter with needle-point display of counts per minute (CPM) and milliRoentgen (mR) per hour
  • Three selectable operation ranges of X1, X10, and X100 for adjustment when peak mR levels are met
  • Red, flashing counter and a beeping noise indicate each ionizing radiation increase event

Product Details

User Manual [301kb PDF]| Spec Sheet [2.02mb PDF]
  • Shipping Weight: 1 pounds (View shipping rates and policies)
  • Shipping: Currently, item can be shipped only within the U.S.
  • ASIN: B004CCRIJ8
  • Average Customer Review: 4.1 out of 5 stars  See all reviews (15 customer reviews)
  • Amazon Best Sellers Rank: #23,787 in Industrial & Scientific (See Top 100 in Industrial & Scientific)
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Frequently Bought Together

Radiation Alert MONITOR4 Analog-Based Ionizing Radiation Detector + iOSAT Potassium Iodide Tablets, 130 mg (14 Tablets) + RADStickerTM peel & stick, nuclear radiation exposure determining dosimeter
Price for all three: $361.88

These items are shipped from and sold by different sellers.

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Product Description

The Radiation Alert Monitor 4 is a hand-held radiation detector with an analog display over three selectable operational ranges for detecting potentially harmful ionizing alpha and beta particles, and gamma and x-ray radiation. This meter has a dual-scale, analog, needle-point display of counts per minute (CPM), and milliRoentgen (mR) per hour. It detects the four main types of ionizing radiation: alpha and beta particles, and gamma rays and x-rays. It has three selectable operational ranges (X1, X10, or X100) to be adjusted when the meter face peaks at the highest mR level.

The Monitor 4 has a red, flashing counter and a beeping noise to indicate each ionizing radiation event. It has a halogen-quenched Geiger Mueller (GM) tube with a thin, mica end window for sensing ionizing radiation. It is used to check radiation levels in the environment and objects, such as particle accelerators, x-ray shielding, and industrial gauges. An audio indicator with an internally mounted beeper can be turned off for silent operation. The Monitor 4 cannot be returned.


Reading Ranges 0 to 0.5, 0 to 5, or 0 to 50 milliRoentgen (mR) per hour, or 0 to 500, 0 to 5,000, or 0 to 50,000 cycles per minute (CPM).
Accuracy Factory-calibrated by pulse generator, with accuracy + or -15% of reading full-scale, relative to Cesium 137.
Energy Sensitivity 1,000 CPM/mR/hr (Cs137).
Detection Alpha down to 2.5 mega (million) electron volts (MeV), with typical detection efficiency at 3.6 MeV at greater than 80%.
Beta at 50 kilo (thousand) electron volts (keV) with typical 35% detection efficiency.
Beta at 150 kilo (thousand) electron volts (keV) with typical 75% detection efficiency.
Gamma and x-rays down to 10 keV typical.
Temperature Range -20 degrees to 55 degrees C (-4 degrees to 131 degrees F) and an internal detector.
GM Detector Halogen-quenched with window thickness of 1.5 to 2.0 mg/cm2. The effective diameter is 0.92 cm/0.36”.
Dimensions Dimensions are 209 mm x 71 mm x 50 mm (8.2” x 2.8” x 1.9”).
Weight 178 g (6.3 oz).
Output 3.5 mm headphone jack for use with observer software (not included) and Windows-based computers.
Normal Background Radiation Approximately 5 to 20 CPM.
Battery 9-V alkaline battery (not included) for approximately 2,000 hours of continuous use in a normal background.

Radiation detectors can detect a broad range of ionizing alpha and beta particles, and gamma and x-rays that may be emitting harmful levels of radiation. They sense ionizing radiation with an enclosed Geiger Mueller (GM) tube to count radiation particles or rays. Alpha and beta particles are measured in counts per minute (CPM) or counts per second (CPS). Gamma rays and x-rays are measured in milliRoentgens (mR) per hour, microSieverts (μSv) per hour, or milliSieverts (mSv) per hour. Alpha particles are positively charged and heavier than beta particles, and have a limited range of approximately 3 to 5 centimeters by air. Alpha particles can be shielded by objects such as paper and unopened skin. High-energy beta particles are electrons, heavier than gamma rays, and can take either a positive or negative charge. Beta particles can be shielded by aluminum or wood. High-frequency (short wavelength) gamma rays are the strongest and lightest rays. Gamma rays are more penetrating than alpha and beta particles. They can be shielded by dense materials such as lead, and large masses of concrete, hardened steel, or water. X-rays are man-made gamma rays, and have essentially the same properties and function. Radiation detectors commonly have either an analog or a digital display. Analog radiation detectors output with a needle-point scale, and digital units generate a numerical LCD digit display. Radiation detectors are commonly used by hobbyists for safety detection and rock inspection, and professionals in the in the nuclear, medical, mining, instructional, and research industries.

SE International manufactures radiation detection products and accessories under the Radiation Alert brand. The company was founded in 1979 and is headquartered in Summertown, TN.

What’s in the Box?

  • Monitor 4 radiation detector
  • Carrying case with belt clip
  • Instruction manual
  • Conformite Europeene (CE) certification

Customer Questions & Answers

Customer Reviews

Most Helpful Customer Reviews
24 of 24 people found the following review helpful
4.0 out of 5 stars sean893 May 6, 2011
By Pocotan
Verified Purchase
Great item to detect alpha radiation not only beta and gamma for this price, and very fast to search higher spot, if you need to connect and calculate its data, i will recommend usb version of this, but it's enoght to check aroud our environment, here in tokyo, japan.
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26 of 27 people found the following review helpful
5.0 out of 5 stars Excellent geiger counter for the money. October 8, 2011
Verified Purchase
I recently purchased the Monitor 4 geiger counter due to the ongoing nuclear crisis in Japan. I have been very pleased so far. It is very sensitive, accurate, durable and easy to use. Plus, the price is fair. I strongly recommend anyone who purchases this geiger to also purchase the Observer geiger software Radiation Alert OBSERVER Software For Collecting Counts From Radiation Detectors. When used together with the software, it turns the Monitor 4 into a very capable instrument. I have been using both together to check for low-levels of food and drink contamination. It has been very useful so far. I have also owned the Inspector+ geiger counter. That geiger counter has a super-sensitive pancake sensor. Only a 10-minute count is required for that instrument to get a fairly accurate reading of low-level contamination. BUT the same thing can be accomplished with the Monitor 4 when used with the Observer software. This can be done by taking a longer timed count of at least 20 minutes (but 30 minutes to 1 hour is even better). The reason the longer timed count is necessary is because the Monitor 4 has a much smaller sensor compared to the Inspector+. But in the end the same thing can be accomplished when used with the software. Plus the Monitor 4 is in stock NOW. The Inspector+ is back ordered everywhere by at least 6-12 months. You really can't go wrong with the Monitor 4 when used with the Observer software. It is a reliable, accurate, and durable instrument that will last many years. Just ask the owners of the older design Monitor 4.
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19 of 19 people found the following review helpful
5.0 out of 5 stars great rugged detector August 1, 2013
By K. grey
I bought this as a field detector 3 years ago to compliment my hikes in Arizona - with no experience on the subject beforehand (I did a stint in particle physics, but those detectors were MUCH bigger). I knew up front it was not the most sensitive detector - but I didn't know what that meant practically.

First, the purchasing. There are two options in the base model, one you can actually assemble yourself and save some cash, the other pre-built and reasonably calibrated. I was lazy and bought it calibrated.

Made in USA of plastic.

It arrived promptly, in perfect condition. It comes with a lightly padded case with a handy clip (for your belt or backpack) sufficient to protect it from 4-foot falls. It works well and the case design allows it to be partially open - holster style - for quick extraction. I lost the case a year ago and really regret that. flashing light, three beep tones (you can turn them off), battery check, and three sensitivity levels (more later).

Basic physical character - It is not tiny, but fits very ergonomically in my hand. weight is 1/2 LB (250 g). Controls are perfectly intuitive, with positive acting slide switches that do not break. It has survived a dozen+ falls without its case, one included bouncing down several flights of rocks. The mica window over the tube has a metal grid which has saved it several times. It is not waterproof. Battery life is VERY long. I have changed the battery twice, ever - but out of paranoia - never once ran out. I'm sure you could keep it switched on for a day or more with a single 9V battery. Extremely robust unit, light enough to hold all day, but not discrete.

Sensitivity is a tradeoff. It has three levels, to 0.5 mR/hour, up to 5 mR/hour, and to 50 mR/hour.
Read more ›
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28 of 31 people found the following review helpful
4.0 out of 5 stars Geiger Counter January 30, 2011
Verified Purchase
This is a good product for the price however it seems it could be more sensitive. Plus the material you are testing needs to be directly in front of the scanner or it will not register to the geiger counter.
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10 of 10 people found the following review helpful
2.0 out of 5 stars Not for serious work - very low sensitivity December 2, 2013
By T400
Verified Purchase
I purchased this device because I am working on radioactive isotope 32P (strong beta) extensively, and I want a personal device that measures me to ensure there is no contamination on me after work.
First of all, it does count. However, it is not sensitive enough compare to a traditional Geiger counter with a pancake detector.
I have compared side by side that when the traditional one used in the lab gives about 1.5k cpm, this Monitor4 does not show any difference compare to background, even when the detector is about 1-inch to the source.
I am not sure about other application, for serious beta ray detection it does not work well.
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14 of 16 people found the following review helpful
5.0 out of 5 stars Superior value and function April 29, 2011
Verified Purchase
You will save a lot of $$ if you buy a modern instrument (like this one) vs an old CD 700 series meter, then have to get it refurbished and calibrated. While not as bulletproof as the old metal CD survey meters, this is new, it's calibrated, and in the long run cheaper.
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8 of 9 people found the following review helpful
4.0 out of 5 stars Good Instrument April 15, 2012
By John
Verified Purchase
I looked at a number of radiation monitoring devices and this seemed to be a good choice for the price. I have a rather old geiger counter that is not as sensitive as this one. My only complaint is that the directions for use comes on a CD and I didn't think was greatly helpful. It is possible that someone with more experience than I have would find the directions more helpful. I am satisfied with this purchase but feel written directions for less experienced users would be helpful.
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Most Recent Customer Reviews
3.0 out of 5 stars Solid performance, but sloppy labeling
I have had one of these (non USB) for about 3 years. It has been very reliable and appears to always function properly (including on materials that max out its range). Read more
Published 5 days ago by John A. Luczaj
5.0 out of 5 stars Great Camping Tool
We go camping in the BLM area in Eastern Arizona. When we saw radiation warning signs by the old uranium mines, I figured we should get this to be sure we are safe. Read more
Published 24 days ago by Gene Chastain
2.0 out of 5 stars Analog needle display not useful under ordinary conditions
The product is described as registering 5 to 20 CPM (counts per minute) "normal background radiation". Read more
Published 5 months ago by Bob
5.0 out of 5 stars Budget detector that can still detect all three (alpha, beta, and...
Pro: cheaper than its brother (Inspector). Con: analog meter - have to count the "beeps" to measure CPM/accumulated readings. Read more
Published 7 months ago by J.Lee
5.0 out of 5 stars Radiation detector
this is an excellent portable radiation detector and works good on testing well cuttings samples, etc. It has accurate readings too.
Published 8 months ago by John R. Gilbert
5.0 out of 5 stars Very Good Detector
Purchased this at about the time that North Korea was saber rattling. We live in Seattle, which is more or less directly downwind from there, so it's worth having supplies on hand... Read more
Published 9 months ago by M. Culver
3.0 out of 5 stars I seems to work
I am not sure if it is really accurated, I have not a ny instrument to make a quantitative comparison
Published 13 months ago by Raymundo Cassani
5.0 out of 5 stars Radiation Alert Monitor 4
This product is exactly as described and it appears to a very high quality product. I would recommend this product and I buy it again.
Published on November 28, 2011 by 20MM
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