Re DM89 CO2 Indoor Air Quality Carbon Dioxide Monitor

GOOD POINTS
- Clear display
- Instruction leaflet clear (though few typo's and grammatical errors)
- NDIR, so compliant with UK Health & Safety Executive recommendation. Also CE marked.
- First impression is that the battery life is acceptable
- Device arrived quickly after placing the order

THINGS I DIDN'T LIKE
- It only measures CO2, temperature and humidity. It is therefore technically does not measure "Air Quality", as stated on the website, as it doesn't measure e.g. particulates
- Although the website says a 1.5sec sampling time, it feels much slower than that. Takes a few minutes to settle out on all parameters, and is significantly slower than another similar device I have (which also measures particulates).
- Although it says it is sensitive to CO2 changes of 1 ppm, there is no indication of how accurate the meter actually is. For example, if there is a 10% error, then a reading of e.g. 500 will be anywhere between 450-550 ppm. Whether this is significant will depend on how the meter is being used. Also no mention of whether the device needs periodic recalibration or whether this is done automatically.
- Website indicates that CO2 of 1001-2000 means that the air quality is "OK". However, I'm not sure where the evidence for this comes from and suspect that it is very inaccurate as the HSE guidance states: "An average of 1500ppm CO2 concentration over the occupied period in a space is an indicator of poor ventilation. You should take action to improve ventilation where CO2 readings are consistently higher than 1500ppm".

The problem is that, at the moment, there are very few really reliable and thorough reviews of CO2 monitors written for assessing ventilation, so you're largely dependent on what information the seller/manufacturer provides, which in many cases, is very little of real use.

BOTTOM LINE
Would I buy it again? Possibly, but not without having a good look at what else is out there.