Quite simply, it is the brains that decides when to activate the air bag(s) and seat belt tensioners (if the car has them) and your life could depend on its ability to make the proper decision.

The control unit measures the forces of decceleration acting on the vehicle. It can tell the difference between normal deceleration during braking, higher deceleration that lasts a very short time such, as bumping a car, and high deceleration that lasts a milliseconds longer, such a ramming a solid object at speed and crumpling the crush zones of the chassis.

Depending on its programming, it activates the seat belt tensioners, if they are installed, and the driver and passenger air bag.


Best Regards,
Jim