I had some enlightening discussions with my son a Linux expert. He insisted that there must be a wrap up of the messages and it's settings.
So next time active on owner I opened the message (from user 'Cams' indicating to app Tapo) and started to press it until (o wonder) more information popped up.
Also I got an installation button on top on the right of the message.
Pushing this button opened a 'new world' of settings just for this type of message. There I could declare my alarm sound and first tests are absolutely positive.
Today I got a false alarm but was not able to track it. I clicked the message away unwanted. Nevertheless the alarm works now for the other user 'Cams' for Tapo when active on user owner and this great news.
It looks that this option is quite unknown in general.