CITROEN DS3 Handbook page 152

Under-inflation detection
System which automatically checks the pressures of the tyres while driving.
The system monitors the pressures in the four
tyres, once the vehicle is moving.
It compares the information given by the four
wheel speed sensors with reference values,
which must be reinitialised every time the
tyre pressures are adjusted or a wheel
changed.
The system triggers an alert as soon as it
detects a drop in the inflation pressure of one
or more tyres.
The under-inflation detection system
does not replace the vigilance or the
responsibility of the driver.
This system does not avoid the need to
check the tyre pressures (including the
spare wheel) every month as well as
before a long journey.
Driving with under-inflated tyres
impairs road holding, extends braking
distances and causes premature
tyre wear, particularly under arduous
condition (high loading, high speed,
long journey).
Driving with under-inflated tyres
increases fuel consumption.
The inflation pressures defined for
your vehicle can be found on the tyre
pressure label.
See the "Identification markings"
section.
Tyre pressures should be checked
when the tyres are "cold" (vehicle
stopped for 1 hour or after a journey of
less than 6 miles (10 km) at moderate
speeds).
Otherwise (when hot), add 0.3 bar to
the pressures shown on the label.