Seat Belt and Airbag

I'm pretty sure a car has a mechanism in which the airbag deploys if it feels a sudden strong fender bender or worse. And yes, even if not wearing a seat belt. Maybe the only connection is when the car feels a strong tug on the seat belt. Every car is different.

Hmm.. then I guess I am having wrong information. Actually I tried to search about the same on internet too, but I have got multiple answers for it. So it makes me even more confused. Some of were even saying that, airbag without seat belt can even harm you. I don't know how, but it is new thing to me.