CITROEN C-ZERO Handbook page 48

Safety
Hazard warning lamps
F When you press this red button, all four
direction indicators flash.
They can operate with the ignition off.
Brake lamps, automatic
operation
The brake lamps may light up automatically
when you release the accelerator pedal.
Their illumination is not systematic and
depends on the rate of deceleration.
46
Horn
F Press the central part of the steering wheel.
Horn for pedestrians
(Depending on equipment.)
System to alert pedestrians to the presence of
the vehicle.
Operation
When the vehicle is started, illumination of
the button indicator lamp for a few seconds
indicates system activation.
https://www.automotive-manuals.net/
The horn sounds when the vehicle speed is
between 0 and 22 mph (35 km/h),
Deactivation
In certain driving conditions you can deactivate
the system.
Press this button.
The button indicator lamp comes on and the
audible signal stops.
Another press reactivates the system.
The button indicator lamp goes off.
Before deactivating the system, make
sure that you are not driving in an area
frequented by pedestrians.
The system is reactivated automatically at
every new start.
Malfunction
The button indicator lamp flashes if the system
malfunctions. Contact a CITROËN dealer
or a qualified workshop to have the system
checked.