CTC1000 Alarm Siren Issue


I’m using a CTC1000 alarm system from Velleman at home and I’m having issues with the outdoor- and indoor siren.
In the past, the indoor siren beeped during the arming exit period (20s) and the outdoor siren didn’t. The outdoor siren only confirmed with a beep when it was armed. Recently, unexplicably, the outdoor siren starts to countdown from 20s to 0s as well, which is very annoying for the neighbours.

I’ve tried all the steps in the manual which all lead to the Devices -> Program Siren -> Confirm Off setting but this doesn’t seem to work.

Does anyone have some idea please?