In a Belt-in-Seat (BIS) system the shoulder belt is attached to the backrest of the seat instead of to the B-pillar between the doors.

This position allows the shoulder belt to better wrap around the occupant's body, thereby increasing the efficiency of the belt system. In roll-over accidents, it also contributes to keeping the distance between the head and the roof.

Moreover, the BIS system is very convenient in the case of removable seats or flexible arrangements.