My parents' home used to have lots of blackouts during a month, mainly on rainy season.
I really wanted a way to monitor these blackouts and know an average of the time without electricity there.
As I had some VFD displays I found for less than a dollar each on a dodgy store here where I live, I decided to make a clock out of it and stuff the blackout detection in it too.
Right now, there's a bug that makes the DS1307 RTC registers being rewritten with trash randomly when blackouts/MCU resets occurs, so it's probably a code problem.
Sure, I could've gone the easy way and used an old smartphone to do this. Just leave it charging all the time somewhere no one would pull it out of the outlet, if it stops charging, there's a power failure. I may even to it later.
I made a simple schematic of this clock. There are some differences to my build, but nothing critical.