This is an amazingly feature packed little device, and very well thought out. The screen is large and clear and backlit, and is put to good use. It even has a builtin gyroscope so it can flip the screen if it is held upside down. You can data log with it, and you can even hook it up via USB to your PC. It charges via USB as well, very convenient.

The included detector tube inside the unit is an M4011, not the most sensitive and it will not detect alphas. But this is a good choice for a beginner and is inexpensive and pretty durable.

The GMC-320+ is reasonably hackable. I just modified mine to accept an LND-7312 which is an exceptionally sensitive alpha/beta/gamma pancake detector. If you have a known calibration source, you can calibrate the device to uSv/h.

Highly recommended.

I purchased one of these units as part of our home safety kit (just in case something really bad happens).
After building a couple of cheap geiger counter kits, I decided that I would like something that was at least factory calibrated and in a nice enclosure. USB connectivity was a must. Also, some of these units are very expensive and cost was definitely a determining factor.

It compares favorably to the other units in its price range (I found about 3). The sensitivity and range for this unit should be good enough to let you know if you are in danger or not. Also, I was very pleased when I checked the battery compartment and found a Tenergy brand lithium ion 14500 battery. Tenergy is top shelf. It's nice to know that it is easily replaceable.If you wanted to use the unit for extended periods of time, you could purchase several of these batteries and replace them as needed. Also, they thoughtfully allow the use of 14500 non-rechargeable batteries, just go into the settings and turn off battery charging. One other feature is an analog out port that allows you to pump the clicks into another device (like your latest Arduino project) using a standard 3.5mm stereo patch cable.

The plastic case is good enough. The buttons aren't bad and the display is decent. The graphic LCD has a backlight that can be set to shut off at a set time interval after pressing the buttons. There are several display modes, text, large text and graphical. I wouldn't want to drop it though. If the unit was in a sturdier case I could give it 5 stars. The unit can store data in its 1 MB storage. It's not a lot, but for text it is plenty. How long it lasts will depend on how often the unit is set to record data. You will fit longer periods of time if you set it to every minute instead of every second (about 60 times longer). My main concern wasn't data logging, but it is nice to know that it is there. I will probably leave it running, although my wife will probably make me turn off the clicking noise at gun point. The good news is that the PC software can be set to sound an alarm at a preset level. This way, I won't get shot and we will still get notified of a dangerous level with the clicking sound turned off.

The PC software is just OK. It does everything you would probably need it to. They include a regular and a "Pro" version. the "Pro" version can do things like send you emails to let you know that the local nuclear reactor has melted down and you should probably pick up the wife and kids and go on vacation somewhere. However, the "Pro" version will run you an additional $9.95 to unlock. I found that to be a bit annoying as I had just paid $118 for the unit. If it was included without the surcharge, I may have given it 5 stars.

All in all, you can't beat it for its price. If you just need to know if the current radiation level is safe or not, this unit may be for you. I would not use it professionally as it does not come with a calibration certificate (which can be pricey). There is a way to perform a calibration in the unit's firmware but you would need access to at least 2 certified radioactive test standards. Another way would be to send it out and have someone else do it for you. I would recommend sending it out if you need that kind of accuracy.

Works great with great battery life. It was unnerving at first because it immediately started to count, but this is normal background radiation. A bargain at this price, worth much more.

A no-frills, hand-held portable Geiger Counter.

Pluses:
+ Functional, fairly accurate, and good response time
+ Lightweight and portable
+ Simple operation
+ Choice of multiple scales, digital, and graphic display
+ Data logging feathre
+ Battery rechargeable through USB port

Minuses:
- Plastic build doesn't feel very solid -- don't drop it
- No external sensor tube; No indication of where the sensor tube is located
- Programming is confusing and not intuitive

For $90 it's not a bad deal, and it does what it's supposed to.
But it's really more of a kid's laboratory demonstration unit, than a professional measuring device.

This is a great little geiger counter (nuclear radiation monitor). This does not read EMF...that is another type of monitor. The GMC-320 measures Beta, Gamma, and X-Ray radiation. The GMC-320 does not measure Alpha radiation but the GMC-600/Plus does measure Alpha radiation. The GMC-320 does not have WiFi connectivity but the GMC-320 Plus does have WiFi connectivity. I am checking the GMC-320 with several types of radiation sources such as: rocks, beads and lantern mantles. I'm comparing the readings to an old Radalert (Model 50 or 100). The lantern mantles are quite energetic. There are all kinds of display modes including graphing. The monitor can interface with a computer. The monitor includes rechargeable batteries and can be charged via USB connection. The monitor measures 3 x 5 x 1" and weighs 4.37 ounces. A great little geiger counter!