Siren makes one really loud beep and that's it

I've not had that problem with mine.  Did it sound like the chime beep or something else?  If you're worried, maybe just change the batteries and test it.

Just a rule out, do you have a smoke detector or CO detector in the same area as the siren? (and not necessarily the SS products) - some smoke detectors might do that with low batteries (usually, they will beep every few seconds to alert you of low batteries, but I guess it's possible some might only beep once or twice, who knows).

The siren it two weeks old.  I will pull the battery and test it.  I suppose if it has been sitting in a warehouse for a year that the battery could be on its way out.

Sometimes, the battery could be slightly unseated (mostly with the button cells), this can occur with nearly all of the sensors (according to sporadic posts on the forum over the years) but the siren with 4 AA batteries doesn't seem likely they are unseated- but if changing the batteries doesn't work, unfortunately, you'll have to call SS, and request a siren replacement.