I looked multiple ideas, I ended doing my own:
I have all my internet devices with UPS battery backups, this includes my security cameras, Smartthings, cable modem, wifi router. Probably I will get a Tesla power wall in the future lol, I have about 10 UPS battery backups.
For the power loss notification, I have the Aeotec energy meter, I setup a piston in webcore to monitor the voltage in my home, if it is less than 90v the battery backups will be using battery so webcore will send me a custom notification to my cell phone. This will be corrected in the future, I have plans to get a automated power generator with its transfer switch. I have a generator but I must connect it. Not the best if someone cuts your power too, but I will have time to see over my cameras before everything dies.
For the cellular backup, the correct term is failover, you want 2 internet providers, in my case I have cable, and the cable is hanging from the pole so it’s very easy to cut it and leave the whole house without security, so I got a multi wan switch, it came with load balancing and failover, you choose, so I used the failover, fortunately my employer pays me a wifi hotspot that I never use, 5GB of free internet, anyway I work at home and I use my cable internet, so I got one of those tiny vonets wifi bridges(I will replace it later with a router with sim card) and configured it to my hotspot, configured the switch so the main internet is cable and failover to the hotspot. It works fantastic, I can control everything. I will receive every notification. It will not consume the 5GB of the hotspot because it will only switch to the hotspot if the cable internet fails. Also the switch has multiple LAN ports, so you can configure it just to get Smartthings and your security cameras DVR/HVR on the failover internet, and everything else with be without internet, I mean, if you just have a prepaid 1GB hotspot, still will work, and the data usage will be less.
Hope this helps, please leave your comments. I’m interested in your opinion.