Just thought I'd share this since we are all in danger of it. I work for a HVAC company and one of our big beliefs is every home should have a CO monitor. NSI 3000 Low Level Monitors are the best out there IMO. Google it and read up on them, I try and install them in every home I go into because of one simple reason, they saved my wife's life this winter! They read as low as 5ppm, and alarm at 15ppm. Most store bought "detectors" alarm at 400ppm, some read as low as 70ppm, and they have to read that high of a level for hours! Look on the back of your store bought detectors if you have them and see how high it has to be before it alarms. Plus the NSI have a screen that shows you how the level of CO is. Trust me I don't work for them or get any spiff for doing this. Actually I lie if I save someones life because of a simple "new thread" that is the best spiff I can get! I really think CO is a problem most of America looks past, and I'm not sure why, well most are uneducated and having been through hours of training it really opened my eyes. Read up on them, and CO in that matter it could save you and your families life some day! I know a lot about them and can most likely answer any question you have on them, PM me if you have any questions.