Where is the best place for carbon Monoxide Alarm?

[Enchanted Cobwebs]

Just putting the carbon monoxide alarm up and a bit confused. The instructions say to locate 15 feet away from a fuel burning appliance, between 4 inches and 12 inches from the ceiling on a wall or on the ceiling 4inches from the wall. Thats all ok but 15 feet away from where I'm working, wouldnt I be dead by the time the alarm noticed? I'd rather it go off too soon and if need be I get an extractor rather than rely on open windows

Where does everyone else put theirs? just thinking my room might not even be 15 feet long! I'm nearly there

Thanks
Helen