To call the emergency services, you should dial 112.
If you are on the slopes and need assistance, you can also dial 112 and state the location (name of the piste and the number on the nearest trail marker/beacon).
You may also be able to find a local number for the Piste Patrol (Pisteurs-Secouristes) printed on your physical lift pass.
If there are several of you at an incident on the mountain, a few people could ski down to the next lift, and let the lift staff know about an incident, and then take the lift back up to the incident and wait for rescue.
Important Insurance Information:
Rescue on marked, open ski slopes is not free in France. You will be charged for the toboggan, snowmobile, or helicopter evacuation. Always ensure your travel and winter sports insurance covers these medical extraction fees prior to travelling. You may be able to purchase rescue insurance in advance from the lift pass office.