Two parts to you answer: 1) Air raid/Nuclear War If by a siren you mean a wailing sound that occurs periodically, typically once a week, on Wednesdays or Thursdays, with regularity, and warbles, then you are listening to an air raid siren that's left over from WWII and the early cold War. (If you want to know that the sound of one is like, watch the movie THE TIME MACHINE from 1960's and you can hear it in the latter half of the movie) The speed of the warbles have different indications. If you have a very slow warble, then it was just a test warning. If the warble cycles no more than twice a minute, it was an air-raid warning, and finally, if the warble cycles several times a minute (you can hear that in the movie) its a nuclear attack alert. Where do you live?!?! I didn't think they had them any more. With the advent of ballistic missles that could be fired and reach their targets in less than 30-40 minutes, the best thing you could do is find a male/female ( whichever you prefer) and at least be vaporized or irradiated in the throws of passion. 2) Emergency I'm assuming you are talking about stationary sirens. Most of the sirens are limited to just a few specific purposes which are: Nuclear Emergency: I live close to the Pilgrim Power Plant in Plymouth, Ma, and they have sirens all over the place. Once in a while they test them and they are high pitched sounds and they are supposed to warble when there is a real emergency. Fire Siren for Volunteers General Emergency/Alert-Civil Defense