In addition to regular smoke detectors in our home, we also have this First Alert combo smoke/carbon monoxide alarm in the hallway outside our utility room where the furnace is located. That gives us protection from carbon monoxide poisoning.
In the event that our furnace may have a carbon monoxide leak, this alarm within close proximity to the furnace would alert us to the danger. It would also alert us in the event of a fire. This is the perfect combination for anywhere you have not only the threat of a fire, but a carbon monoxide leak also.
It has a loud alarm, that would easily wake us. This alarm has photoelectric smoke sensing, so it doesn't go off every time I cook, it somehow knows the difference. I used to have a regular alarm in this spot, which is right by the kitchen and it was always going off (I'm not the greatest cook). Anyway, this alarm doesn't go off unless it gets real smokey, and if it does, it has a mute button. The alarm chirps when the batteries need replacing and it has two indicators that will light for either carbon monoxide or fire alert.
This alarm makes our family feel safe.