I managed to set mine off a couple of weeks ago, I forgot to open the car and started jacking it up to take the wheel off and the alarm went off.
I agree it's not that loud. People hardly take any notice of alarms on cars these days anyway, It's loud enough so that I could hear it in my house but certainly not deafening. I think there are rules over how loud alarms can be in some countries, something to do with noise pollution.