Many people make assumptions about how they will, or should respond in a fire. One assumption is that if you have a built-in fire alarm system in your home, you don't have to call 911. This is not true.
If you have an automatic alarm system (and it's working), the system/service will notify the fire department that a detector in the home is activated. This will generate, in most jurisdictions, an automatic alarm response which is usually 1-2 vehicles (compared to 4+). Most automatic alarm calls are false alarms (for a number of reasons). Usually, fire departments will respond with the same speed as a 911 "Report of Fire", but mentally many firefighters' first thought when they hear automatic alarm is "it's probably a false alarm". As a result, the firefighters while responding quickly, often are not as mentally prepared to battle as they would be for 911 "Report of Fire". This is definitely true for me too.
I know that making assumptions about automatic alarms has killed many firefighters, but my experience also tells me that false alarms are extremely common.
Safety Squad suggests calling 911 always... either after you've escaped danger or if you're trapped. First, You will at least double the number of firefighters responding (because 911 knows it's bonafide). Second, the firefighters responding to a "Report of Fire" assume it IS a fire and not a false alarm. Third, if you are trapped, you can communicate to 911 where you are, how many people are in the home and any information that may help firefighters find you.
When we know that people are trapped, the level of alarm escalates, our determination rises and given a place to look, we will walk through walls to find you.