Make a decision
CO alarm versus furnace inspection
One scope
An alarm warns occupants of dangerous carbon monoxide under its operating conditions.
The other scope
Inspection aims to find faults in the fuel appliance and venting before an event.
A concrete example
A family can test alarms on schedule and still need a registered contractor to inspect the furnace. A service record does not justify removing or ignoring an alarm.
Which question settles it?
Both matter; an alarm does not certify the furnace, and an inspection does not replace alarms.