Is there a way to get notify when mobile network is unreacheable? Sometimes mobile network (cellular network) is unavailable for my phone and I won't be informed about call attempts and SMSes. Is there a way or application that notify me (by notification, vibration, sound, etc.) when mobile network is unreachable?
I'm using Android 4.1.2

EDIT: By unavailability of mobile network I mean any reason that makes that I cannot call to anyone and others cannot call to me e.g. be in out og scope of cellular network, removing SIM card or anything.
I like OpenSignal, it will notify you when you leave a coverage area and also help you figure out the best service provider in your area.

https://play.google.com/store/apps/details?id=com.staircase3.opensignal&amp;hl=en