We've had a bunch of power outages at the cabin recently. The big one of two weeks ago as well as some blips that only lasted a few seconds but were enough to mess up the digital clocks or triggered the PF (power failure) notation on appliance read-outs.
I picked up an old analog plug-in clock.
It stops when the power goes out, restarts when the power comes back on.
I can now take actual time, subtract the time on the plug-in clock, and have some idea how long an outage (or outages) have been.
Yes, if I'm gone for a while, I can't tell if there's been a single outage or multiple ones. And things get complicated as well if an outage is more than 12 hours, but those are the very rare exception.
Most the power outages are of short duration. But now I have a way to determine if they've run longer, helping to determine if refrigerated food might need to be checked, or if I might want to consider beefier battery back-up power supplies for stuff like Internet or my cell phone booster.