Side airbag system including an airbag arranged to deploy in the event of an impact into a side of the vehicle, a side impact crash sensor arranged to sense an impact into a side of the vehicle, and an inflator for inflating the airbag. The crash sensor is an electrical sensor which includes a movable sensing mass which moves when the side of the vehicle is impacted and a signal generating mechanism for generating a time-varying signal representative of movement of the sensing mass, analyzing the signal representative of the movement of the sensing mass and generating a deployment signal based thereon. The inflator is coupled to the crash sensor and receives the deployment signal therefrom and inflates the airbag upon receipt of the deployment signal.