Or just get a $5 radio doorbell. You know, when it's 'urgent, right now' you don't want to learn what you are too late because for whatever reason internet/wireless/cellular wasn't working.
This ^ anything else is just wanting to play with tech instead of solving the problem immediately. Which is fine, sure, but that radio doorbell (or better, 3 different ones for different priority levels, since it seems important) will fix the issue right now.