Its definitely the powersounder.
I originally replaced it because it kept going off on its own, all was well for a few months then it started again and the light was flashing when armed. Checked the powersounder and it had gotten wet somehow notsure.gif so took it back to Vaux, told them it was broke and got another one for free 🙂 Haven't got round to replacing it yet but have removed my old one hence why my light is flashing all the time.
Does anyone know if there are two alarms/ sirens on the Astra SRi? I haven't got my powersounder on yet when i locked my mrs in the car by mistake the other day and my alarm went off...there must be another siren somwhere in addition to the unit beneath the nearside arch.