Notifications/App Running in the Background

So i have a question for everyone. I have had my Hubitat for few months now and really starting to like it. I am trying to better understand a few features that utilize the mobile app/phone. I set up a smartthings water sensor with a small relay that plug into the outlet. The relay will trigger when the power goes out and will trip the smartthings water sensor. This then sends me a notification that my power to my freezer went out and at what time. I test every once in a while to make sure its working. I tested it this morning and noticed i never got a notification. I then realized that my hubitat app was closed/not running in the background on my phone. So my question is if the app gets closed then geo fencing, notification, ect wont work? Does anyone know how to keep an app running in the background ever when closed?