I arrived home today from running some errands to find that the carbon monoxide alarm in my garage was going off. The display was reading 55 ppm CO (which I gather is a non-lethal but nevertheless high reading).
The garage is detached from the house and has no heat. There are several pieces of gas-powered lawn equipment stored there but nothing has been running running. I was gone from the house for several hours so I assume any exhaust from the car briefly running in the garage had dissipated. (When I left the house I just started the car and drove out... no remote start or idling in the garage.)
Does anyone have any idea what the cause of carbon monoxide might be? The CO alarm is less than a year old but maybe it is defective?