Toyota Prius Owner's Manual page 118

1-4. Adjustable components (seats, mirrors, steering wheel)

Adjusting the seat belt shoulder anchor height (front seats)
Seat belt pretensioners (front seats)
118
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Push the seat belt shoulder
anchor down while pressing
the release button.
Push the seat belt shoulder
anchor up.
Move the height adjuster up
and down as needed until you
hear a click.
The pretensioners help the seat
belts to quickly restrain the occu-
pants by retracting the seat belts
when the vehicle is subjected to
certain types of severe frontal
collision.
The pretensioners do not activate
in the event of a minor frontal
impact, a side impact, a rear
impact or a vehicle rollover.