John Robertson wrote:

One can always get a battery powered fridge alarm - I have it on our
deep freeze, but my wife doesn't want it on the house fridge as she
doesn't like the look of it...

Or you can make Pimpom's blackout alarm (link is still good):

S.E.D. 12/29/17
Pimpom wrote:
I made this little gadget for myself several years ago and have
been using it ever since. How quickly can you tell what it is and
how it works? No cheating! :-)

https://www.dropbox.com/s/99sfbr7fms...is_it.png?dl=0