I don't think thats a good idea
I had a car crash where i hit an oil patch spun 3 360's hit a concreate curb then slide across the other side of the road onto 4 lanes of oncoming traffic.
What happened? nothing bad i just had to get new wheels and some wheel bearings (cost over $2000 all up when there wasn't a scratch on the car)
But when my wheels hit the curb the fuel cutoff switch triggered.
Now if yu have this type of accident which is possible or some type where it triggers the fuel cutoff switch then you will be calling 911 for no reason at all.
I think you should maybe have a timmer like 30secs after the sensor has been triggered you get a choice of saying yes or no for the call to 911.
Also if the accident happens you should maybe have a voice recording to tell them that you'r had a car accident then send them GPS info then using D3 or something else sending them the street name the suburb/city and maybe the number
I still don't like the idea of it being auto calling 911