The crash sensor

• The side impact airbag is activated when the crash sensor in the side panels sends a signal to the car's engine that a collision has taken place. The sensors in the side of the car measure the intensity of the collision. When it is severe enough, the airbags get set off.
  
  

Deployment of the air bag

• The airbag sensor receives two signals from the engine in order to inflate. The second pulse shows that a significant crash from the side has taken place. At that point, a signal is sent through a wire to a device called the squib inflater, which ignites the air bag propellant, fills it with nitrogen and sets the air bag in motion.
  
  

Deflation

• The air bag will start deflating within seconds of the impact. There are small holes in the bag and the nitrogen is dissipated through those holes. You will notice that your car is filled with smoke and powder. That's because the manufacturer has coated the air bag with talcum powder or corn starch. That keeps the bag from getting stuck to itself while it sits for months or years at a time waiting to be deployed.