System alert window for an Alarm Clock

I’m trying to develop an Ionic app that needs to activate an external alarm, something like a system alert window that can be activated in front of all the other apps in my device (Android or iOS).

I already tried with Local Notifications, but I need something more striking that can help the app to remind the user of really important tasks, even if the device’s screen is turned off.

Any ideas on how to start this feature or what plugin can I use to develop this?

+1, i have same question, anyone can suggest? Thanks in advance!

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