Set Reminders.app alert sound to Constellation and you can't miss them.

I had one job. I had to put my daughter’s laundry in the dryer. Since I know I’m demented I set a Reminder. Which I never saw because I didn’t look at my phone and the tiny ding went unheard (and perhaps because Reminders sync to El Cap is unreliable).

It’s not the first time I’ve missed a Reminder. When I set one I really want to be reminded.

An alarm option for Reminders would be great but for now there’s a workaround. In Settings:Sounds:Reminder Alerts [1] choose “Constellation” ring tone. It goes on endlessly.

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[1] Same option can be found in Notifications. iOS changed settings model from a hierarchy to an acyclic graph; settings now appear in multiple places. I think this is a good thing, especially with search. Search is still odd though; if you search on Sounds you find individual Sound settings, but the Sound menu item appears with the description “Lock Sounds”. (I think this is a bug.)