Advanced technology -> Safety belt tensioner for Your BMW Z8 Roadster First Generation (2000-2003)

Safety belt tensioner  
153n  
The safety belt tensioner responds to  
severe frontal collisions by tightening  
the belt to ensure that occupants  
remain firmly positioned in their seats.  
A gas-pressure system retracts the  
buckle assembly to tension the  
shoulder and lap belts within fractions  
of a second. This reduces the tendency  
to slide under the lap belt.