Ours are tested every saturday at 10 am...last saturday when they were tested, they went off about 4-5 times.... crack sirens or something.
Just to make a little modification to what my BROTHER said (yes, AirmaN is my younger brother):
The civil defense sirens are tested the FIRST Saturday of the month here in Douglas County (NE).
On the FIRST Saturday of April, both a monthly and annual test are conducted to make sure they are ready to go for the season. Last Saturday, yes, I do remember hearing them sound SEVERAL times between 10am and noon, and, yes, this is because some sirens were not working properly. Some were not working at all, while a few were not rotating.
A couple years ago the Douglas County Emergency Management Agency purchased a BRAND NEW siren system, replacing the older units that were used back in the mid 1900s for civil defense. The sirens, themeselves, are more "attractive" looking, and I guess a computer exists where a 911 dispatcher or the emergency manager can choose which area to sound the alarms.
Fortunately, there was only death, but it was someone who was outside and had no idea what was going on.
That's the intended purpose, for those who do not know, to warn the public OUTSIDE. Having a weather radio to alert you to threatening conditions when INSIDE is the best bet. In fact, sometimes I can only hear a very faint siren while inside a private residence. I have a good idea that if you were in an office building, espeically the interior sections of the building or in a noisy shopping mall or store, you would not hear a PEEP of the sirens.