Paris is full of unusual little quirks, and that’s why we love it. But one of the most arresting, and definitely the most audible of these has to be the eerie sirens that test their lungs without warning every first Wednesday of the month, blanketing the city in sound.

You’re walking down the street, perhaps on your way to peruse some cultural delight or another, or maybe the lunchtime gurgle has kicked in hard and you’re contemplating parking your bottom at a café somewhere before the midday rush to satisfy your hunger.

As the clock strikes twelve, a curious wailing fills the air and lasts for a few minutes, giving you ample time to be confused, eyes darting around to make sure that this strange noise is in fact penetrating everyone else’s ears, and not just yours. It’s a sound you know, eerily familiar, yet it somehow doesn’t seem to belong in this context.

Ten minutes later, at 12.10pm on the dot, it happens again, and you wonder if the city is falling part and you should be running in the direction of safety, wherever that might be (and you never thought to ask…). Your eyes scan the crowds again, but hardly anyone seems to give the strange siren another thought.

And then… you make a mental note to ask someone what on earth it was the next time you think of it. And then, you never think of it again. Until the next first Wednesday of the month when you find yourself still none the wiser.

The good news is that one day I actually remembered to ask someone what it was, and so now I can pass on the wisdom. The sirens are in fact original air raid sirens, originating from before World War II, and still operate as an emergency population warning system, ready to warn us of any impending danger that might befall the city (like if we ran out of baguettes, say. Only kidding). The system is tested once a month to make sure everything is in good working order, and all in all, there are over 4,500 sirens throughout France that exist for the same reason.

FYI, if the sirens do actually sound at a time other than 12pm or 12.10pm on the first Wednesday of the month (ie. in a real-life emergency), then apparently we sit tight, stay calm and wait from further instructions from the police, city authorities or the local TV and radio stations (and no doubt Facebook and Twitter, right?).

But let’s hope it never comes to that. For the practice signals, all that we can do is appreciate a very unique part of Paris’s aural history, and try to imagine what it might have been like to be in the city way back when. And as soundtracks go, you can’t get more authentic than that.

Post originally published 04/02/14