My email/text notifications are similar to others: Power out to each of my EBs or Apex, tank or sump temp too high or low, pH, salinity, and orp too high or low, leak on floor in front or back of my tank, sump level too high or low.
I also have a small (fairly inconspicuous when not lit) blinking LED on the side of my tank cabinet in my usual easy chair line of sight that goes off when any of my pumps are off except during feeding cycles, or those same "big problems" as I call them exist ... Just in case I don't check email or my phone is in the other room and I've messed-up something and not turned it back on after fiddling with my tank. My tank UPS will scream if power is out... louder than the Apex Display, and my Apex Display will play its little tune otherwise when there are big problems.