I haven't actually heard the alarm on my st so I don't know what it sounds like, although I'm sure I can remember saying before about it being quiet.
Possibly the worst (or best for attracting attention if you want to look at it that way) alarm I've know was on my Rover Metro a few years back, the alarm was basically like the horn sounding only mulitiplied about five times. I discovered this at 5.30 am one Monday morning when I was about to set off back to uni and forgot to turn it off before unlooking the boot.

Lets just say I didn't make myself popular with the rest of that street!
