I alerted Bob to this, he got up, looked at the detector while I went downstairs to Google CO Detectors. When I came back upstairs Bob was in bed! I'm like, "You can't go back to bed!" He responds, "It's 4:30 in the morning!" I respond, "If the house was on fire would you go back to bed because it's 4:30 in the morning?" He got up.
Carbon Monoxide is colorless, odorless and regarded as a silent killer. We called 911 and the fire department came out with their CO meter. It recorded zeroes everywhere while we stood outside on the porch. It was concluded that our detector needed replacing. Apparently they are only good for five years. The things you learn, standing outside in the cold, with four firemen.
So the lesson for today is to LISTEN. Not only to the outer noises that alert us to something not right but to the inner voice that tells us to check it out, whatever that "it" might be. In this instance, in hindsight, it looked like we had nothing to worry about but there is always a blessing in every circumstance. Maybe it was just to buy a new detector today. And maybe it is to respect the monitors we have in our home.