Yes it’s true that my first post said I wanted them through the phone’s speaker, but I think I pretty clearly thereafter said I modified that goal to wanting the notifications to come through selected Alexa (Echo) speakers so that others in the home might also hear the notices, and I believe I have now found a way.
As an experiment, last night I turned off notifications for the phone app for one of my security cameras, and substituted an Alexa Routine making an announcement, triggered by motion detection by that camera. It seems to be working perfectly as family members created some traffic across that path, and the designated Alexa devices announced but my hearing aids remained silent other than passing along the announcement at normal, non-jarring volume. What a relief!
So while I was hoping for a one-click solution, this one will involve only the additional effort of creating a few more motion-triggered Alexa Routines while turning off notifications on the camera’s phone apps.
Often, seeking assistance online from fellow users also further stimulates one’s own creative juices, and perhaps this dialog might also prove helpful to others bothered by these jarring in-ear motion detection notifications.