France operates a four-colour alert system called Vigipirate. The levels (in ascending order) are:
Yellow Police are reinforced by other security forces (gendarmes and army) for patrols in train stations and airports as well as on underground railways. Water distribution companies are ordered to take special security precautions. Air defence systems go on reinforced alert.
Orange Security patrols for train stations are extended to TGV rail tracks. General aviation (aeroclubs) activity is limited. Special measures adopted for purification of water.
Red Spot ID checks at train stations. Patrols aboard TGV trains reinforced by gendarmes, military. Limitations on air space. Extra water supplies are set aside by authorities.
Scarlet Includes ban on air traffic and no trains allowed in tunnels. Ordinary water distribution by pipeline halted and replaced by supplies distributed by government from tankers.