How to 100% prevent Android app from closing?

Question

Android

Example: Android system alarm. For some, it rings even when the phone is turned off. And I download another alarm clock on the market - the application can close without saying anything, and sooner or later I will oversleep something important.
How to achieve guaranteed impossibility to disable for custom reminders?

Answer 1

Look for an alarm clock application that can keep its icon in the status bar - the system does not close such applications.
I myself suffer from the same problem, but not with an alarm clock, but with instant messengers:
Viber, for example, can show itself in the status bar and never closes;
And that the vatsap was closed, I only find out after the call and the opponent's question "why are you not answering."

Answer 2

Android has an AlarmManager for such purposes, if the question is about development.

Answer 3

Perhaps you need energy saving, because many devices do not receive notifications for this reason. You can also "Lock" (like that's what it's called) the application so that it doesn't close. Windows button -> click on the application, and there should be a lock. (Does not work on all devices)

Answer 4

The phones of many manufacturers have several programs built into the OS to optimize the phone (such as "Phone Manager", "Security", etc.). They block applications from running in the background. You need to allow everything in them for the application that you need.