I figured some of our UK friends might appreciate this:
https://goo.gl/maps/3sE9HKV1eH32
I was prodding around in London on maps and I found this siren near Waterloo station. I am not sure what model it is (Sorry lads, not a UK siren expert!). It almost makes me wonder if it is WWII era or Cold War era, and if any more sirens are still floating around London.