To calculate the overall star rating and percentage breakdown by star, we do not use a simple average. Instead, our system considers things like how recent a review is and if the reviewer bought the item on Amazon. It also analyses reviews to verify trustworthiness.
If you are in need of an accurate CO monitor, this is worth considering. But while it does provide an accurate measure of CO, all the other options are misleading or presented to the user with incorrect statements. First and foremost is the max button, which is really only a hold button. This unit does not store max values, so pressing the max button does not return max values. That was why I bought this one, and considered returning it when I discovered the false advertising. The other aspect of this that I do not like is that it will only be accurate for two years. This is an expensive unit to buy every two years.
See other reviews: "Only good for 2 years!" and "Beware of the 2 year life"
Nice unit. Returning it. BTW:15% restocking fee!. Not recommending for typical home user not needing PPM readings. Recommend seller update product description for to add expected life (and calibration)--help us save on future customer returns by letting buyers know it needs pro-service, has maintenance limits. As of Dec 2015 Amazon's description didn't hint about limited life... I found out after unboxing and reading instructions, sensor(s) have limited life, after 2yrs either needs re-calibration every 6 months at $39+ your shipping cost, or $59+ to replace sensor. So after two years it would cost me average $30+/yr upkeep assuming I get sensor sensor replaced every 2yrs. Calibration not trivial: two-point cal, (1) zero-cal; then (2) 50ppm CO cal (needs special gas/equipment). For me, knowing PPM is desired, but not worth it. I'll replace it with a home-grade Kiddie or similar (p.s. I have a CO2 meter with PPM display, it self calibrates).
My impressions on the Sensorcon--positive: seems built well, made of metal, professional grade, good off-the-shelf price at 119 usd, made in USA, industrial metal double-clamp belt-clip mechanism. Unsure of sensitivity--I turned on all stove gas burners and it registered zero, closed flue on gas fireplace--still zero. Put it 1ft from car tail-pipe and it registered ~1000 (cold start), and zero after ~2 minutes. But I like it. Would keep if used for work.
From support a Sensorcon dot com: "Both the calibration due and the EOL warning are clock based functions and do not have any bearing on the function of the sensors. The sensors have a life expectancy of 2-4 years so the EOL is set to go off at the beginning of that time span. The EOL will toggle back and forth between the warning and the ppm reading. When the sensor does fail you have the option of doing an out of warranty repair for a new sensor for $59.00. Most other units on the market of this size and durability are several hundred dollars and are typically "throw away" units meaning that when the sensor fails it would be discarded. If you have any other questions please let us know and we will be happy to answer them for you." (this addresses previous comments by reviewer "T. M. Olinger" and others. BTW this was from a quick email Q&A asjubg "does the unit still function when the "EOL" display-indicator kicks in?" )
Tested and returned: Jan 2016. "Sensorcon Inspector" CO meter" Tough, Waterproof, Made in USA: Carbon Monoxide Tester & Meter (CO Tester & Meter) - CO Inspector, Portable CO Detector Meter & Tester for Monitoring or Analyzing CO