CITROEN C4 PICASSO Handbook page 58

Access
Deadlocking
Deadlocking renders the interior door
controls inoperative.
It also deactivates the manual central
control button.
Therefore, never leave anyone inside
the vehicle when it is deadlocked.
56
By the doors:
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 or the locking control
located located on the right of the tailgate,
to lock the vehicle.
F Within five seconds, press the door handle
or the locking control located on the right of
the tailgate again to deadlock the vehicle.