In an impact of sufficient severity, the airbag sensing system detects that the vehicle is in a crash. In the case of a "rollover capable" roof-mounted side impact airbag, the sensing system detects that the vehicle is about to roll over. The sensing system triggers a release of gas from the inflator, which inflates the airbag. The inflator, airbag and related hardware are all part of the airbag modules inside the steering wheel, instrument panel, the side of the front seatbacks closest to the door and the ceiling of the vehicle, near the side windows.