Bring activity in front of all running application

I developed an application such as a reminder reminder, so when an alarm is triggered, my broadcast receiver triggers one action and starts one notification, and also starts one service, it works well.

But when I work in another application for a while, my service and notification are quit, but the activity is not open. this does not happen once all.

So, how can I give priority to my activity so that it can always open if we are working on another application, like on the screen of a call receiver.