Lexus RX400h2006 Owner's Manual page 202

Rear seats
To raise the head restraint, pull it up. To lower it, press the
lock release button and push the head restraint down.
Rear center head restraint — When an occupant sits on the
rear center seat, always pull up the rear center head restraint
to the lock position.
The head restraint is most effective when it is close to your
head. Therefore, using a cushion on the seatback is not
recommended.
OCCUPANT RESTRAINT SYSTEMS
CAUTION
D Adjust the center of the head restraint so that it is
closest to the top of your ears.
D After adjusting the head restraint, make sure it is
locked in position.
D Do not drive with the head restraints removed.
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