Product review (5 stars): Great working CO2 monitor
I purchased this to monitor CO2 levels in a small grow area and it seems to work very well.  It is quite sensitive and you will definitely notice a change if you are breathing near it.  After reading the manual the alarm was quite easy to set although it does use some useless menu names like "P1.0" to describe the upper alarm limit and so on.  The only problem I have noticed is that you have to push the buttons quite hard to activate them.  You can press a button with a normal amount of force and you will feel it go down and hear a click but nothing will happen on the device unless you mash it harder.  Mine is still brand new so perhaps this will loosen up slightly but I doubt it.  Bottom line this monitor is cheap and works great.