If a vehicle was involved in a traffic accident, all used seatbelts need to be replaced, even if damage is not visible.
Seatbelts need to be checked occasionally to determine potential damage. Do not use aggressive cleaning agents since they may weaken the belt.
Special clips that supposedly increase comfort prevent automatic tightening of the belt and are therefore very dangerous. The belt is not tightened when using such clips and so can cause severe injuries in an collision situation.