Who do you call when there is actually carbon monoxide in your home?
The fire department is the appropriate place to call for a carbon monoxide situation. I would call their non-emergency number and ask them to come by at their convenience. If you are in a building with other occupants it's possible the situation is caused by something elsewhere.

FYI most carbon monoxide detectors have a limited life (~7 years). There should be an expiration date on the back. Older CO alarms were extremely sensitive, e.g. to a puff of cigarette smoke or a little bit of fumes from a gas stove. Modern ones have a time-delay function where they will wait a bit, depending on the level they detect.