I recently purchased a $300 or so generator for this purpose. After a brief incident several weeks ago, where Bobby was able to help out and let me borrow his, I decided to get my own.
if the power goes out, you don’t necessarily need to know about it right away. Many tanks should survive fine for at least a few hours, up to a day. I’m not saying it will be good. But I doubt most tanks would crash or livestock loss over a few hours. Obviously, the sooner you recognize and take action, the better, healthier, and happier everything will be. Also, the more peace of mind that you will have.
The brings to question, what if the power goes out while you are on vacation? In that case, I would suggest in Apex, and a local friend that is willing to help. One of my neighbors and fellow reefers here has a spare key to my place.
In the past, with no Apex, I gave a key to one of my neighbors that knew nothing about aquariums when I had to leave the country for a month. Auto feeders and other systems maintained everything just fine. I asked her to check inside every two or three days, and explained what a normal tank would look like. She was to text me if anything ever looked suspicious. And she did. I was overseas, but I did a video call with her, and walked her through doing a water change, with water I had already prepared in case of an emergency such as that. All was well, and no livestock loss except for a coral frag that my goby buried in the sand.