In reply to peebles boy:
I think 'air raid' siren might just be the wrong word there! There was a time in Vallorcine (and every other small commune with a voluntary fire service) when the siren that alerts the Pompiers to an emergency was tested at 12:00 midday every Saturday. As far as I know they haven't done this for some years now. Chamonix, being a considerably bigger commune has a permanent professional fire service, however, I'd imagine it was some sort emergency related to them.