Thank you - I did this and the sounder stopped. I also did 1234# which cleared the internal sounder.
The tamper light is still on (even after putting the lid on and using 1234/1234# again).
I do not have an user or installer manual so now I'm a bit stuck as to how to proceed. My own alarm code...
The alarm was not set but at 3am (friday night) it went off (internal & external sounder). It could not be cleared and the user code did not work. On closer inspection I realised that the panel was very hot and I disconnected the mains power and the panel just died. But the external sounder...