Alarm problem

[S B C]

My alarm went off last night, probably caused by the rain.
The problem is that the siren wouldn't switch off. The alarm kept resetting itself but then restarted almost immediately. Operating the key fob had no effect. I even started the car and the alarm kept sounding.
Then it stopped. Now, the central locking works OK, but there is no bleeping sound to confirm that the alarm is set
Any ideas guys?

Chris.