CITROËN C4 Handbook page 146

Safety
Seat belt not fastened / unfastened
warning lamp in the instrument
panel
When the ignition is switched on, this
warning lamp comes on in the instrument
panel if the driver and/or the front
passenger has not fastened their seat belt.
From approximately 12 mph (20 km/h)
this warning lamp flashes for two minutes
accompanied by an audible signal of increasing
volume. Once these two minutes have elapsed,
this warning lamp remains on until the driver
and/or the front passenger fastens their
seat belt.
144
Seat belt not fastened /
unfastened warning lamps
display
1. Driver's seat belt not fastened / unfastened
warning lamp.
2. Front passenger's seat belt not fastened /
unfastened warning lamp.
The corresponding warning lamp 1 or 2 comes
on in red on the seat belt and passenger's front
airbag warning lamps display, accompanied by
an audible signal and a message in the screen,
if the seat belt is not fastened or is
unfastened.