A shelter window over a rainy city, and a console of dials beneath it. Pull the breaker lever and a civil-defense siren winds up — two tones a minor third apart at 515 and 618 Hz, generated live in Web Audio rather than played from a recording, the horn sweeping once every 15 seconds. Rain and thunder carry on underneath, the shutter and the CRT monitor are yours to play with, and the whole thing is MIT-licensed.