I have three Nighthawk Carbon Monoxide detectors. One in the
basement, one in the kitchen and one in an upstairs bedroom. The
kitchen and bedroom detectors have been showing "10" for the past 48
hours (the basement reads "0"). There is an attached garage, but
neither car has been running for the past 14 hours. I decided to
turn off the furnace and water heater for a couple hours and open four
windows. There was no change in the readings. I then unplugged them,
plugged them back in, and waited an hour. The readings of "10"
returned. Since there is no combustion I"m wondering where the
detectors are picking up the CO? There are no noticeable odors in the
house, even after being outdoors for 2 to 3 hours. Any ideas?