CITROËN C3 Handbook page 64

Access
Deadlocking
Deadlocking renders the interior door
controls inoperative.
It also deactivates the central locking
button on the dashboard.
Therefore, never leave anyone inside
the vehicle when it is deadlocked.
62
F With the electronic key in the recognition
zone A, press a finger or thumb on one of
the front door handles (at the markings) to
lock the vehicle.
F Within five seconds, press the front door
handle again to deadlock the vehicle.