I have a high-sensitivity CO detector.
Been reading 000 for years.
All of a sudden tonight, it went off at 15PPM.
House has been closed up tight all day.

I replaced the battery and moved it to another room.
Reading gradually went back to zero.
Furnace is off, but I turned off the gas anyway.
Don't have anything else that burns fuel.

So, I opened the windows, turned on the exhaust fan
and the reading went up.
So, took it outside and it reads 28PPM.
There's a light breeze, so any local source oughta dissipate??

I can't think of a detector failure mode that would
explain the readings.
I have two other standard-sensitivity CO detectors that
remain silent.

So, is 28PPM high for an outdoor reading?
Can't think of anything I could do about it anyway.