How can i make myApp show the alarms to the user at a specific

I want to make myApp show the alarms to the user at a specific time and appear on the screen just like the system alarm clock, i tried, but did not succeed because if the user closed the app completely then ends (BackgroundMode) also i tried (LocalNotifications) it does However, the notifications do not last for only a few seconds, and this is not true as a alarms.

What is the solution? Please help me because my application depends on alarms completely