Bests & Worsts Reviews from Amazon

I ordered this to verify one (another brand CO detector with meter) I've had went off several weeks ago. The one that I had in the house for more than three years went off and showed around 40 PPM. Since it was over three years old, I thought that it was possibly bad. So I went to Wallmart and bought a cheap CO detector without a meter. I thought I was safe, because the new one never went off. Then I read that it will not alarm until it gets to 50 PPM. I decided to buy this Kidde CO meter. My old CO detector went off again and showed about 30 PPM this time (not as cold outside during this day). I looked at the Kidde and it showed 20PPM (the Kidde alarm did not sound an alarm though). I called 911 and the firemen came to my house and took readings with their meter and showed 19 PPM. They turned off my furnace and the gas. The gas company determined that my forced air gas furnace was blowing CO throughout the house, because the furnace heat ex-changer had holes in it. They said that CO builds up in your body and is potently lethal. I actually feel physically much better now that my furnace is fixed. Sure glad I got the CO detectors WITH a meter.