Seat Belt PRETENSIONERS
WARNING: This page is about a different car, the 2002 Saab 9-3. However, it is still accessible from the selected car via links, so may be relevant.
Seat belt pretensioner is pyrotechnic device, which is detonated by air bag control module. This reaction produces quantity of gas that pushes a piston down inside an aluminum tube. The piston pulls a cable attached to seat belt roller and tightens the belt.