What is the French emergency service number?

There is no single number. 17 gets you the Police, 18 the Fire Brigade (who also do First Aid). For medical emergencies, 15 works over most of France. Finally, there is now a Pan-European number, 112, which works for all services, but necessarily more slowly. Suppose you want more than one service? a car accident, for example, might need all three. Don't worry. Call one service and they will automatically notify the others. French people have over the years formed the habit of calling the Fire Brigade for everything except a burglary, and letting them decide whether to call the cops.