I was working in my basement office yesterday when the upstairs CO/smoke
detector started yelling its CO warning. A few seconds later, the
interconnected detector downstairs chimed in (the thing is REALLY loud).

Fire or smoke would be easy to confirm, but with CO, the only option I
had was to take its word for it.

I called the guys who service our furnace and they said they only have
equipment to measure CO in the exhaust of gas appliances, but they'd
still be happy to make an "emergency" call for the modest charge of $150
plus normal charges.

I then called the fire department's non-emergency number for advice, but
they only have one response for such calls and a few minutes later a big
red truck was sitting in front of the house, blocking the street. Four
guys with handheld CO detectors fanned out through the house and quickly
confirmed a false alarm.

I don't know if I'm going to get a bill for this exercise, but it
certainly wasn't without cost.