My (current) solution is the Zooz ZAC38 Range Extender. It has a battery that charges from the line to keep it alive if the power goes out–which sends an event to the hub and, assuming the hub & Internet are on a UPS and still operational, can send you a notification–or execute whatever else you want done in the event of a power failure.
After a particularly painful experience this year with needing a sump pump we didn’t have (our house, like all in the neighborhood was built with a sump hole, but no pump), this is our solution. The sump hole has been bone dry for several years, but this spring in New England there was a combination of freeze/thaw cycles, a Nor’Easter, and plenty of rain. (Luckily, I had a water detector and our daughter, who lives close by found the wet basement before mold began growing.)
So, the ZAC38 is plugged into the same outlet as the sump pump and, in conjunction with yet another water detector, should tell us if the pump ever fails again!