On the first Wednesday of every month the air raid sirens are tested. This has happened every month since world war 2.
Most Parisians can tell you why, when, how bla bla bla. Not one single person can tell you what to do if it goes off at any other time. Stupid people I tell you...
Here are some photos...
http://www.members.westnet.com.au/kmcdonald/paris3/