Almost all cheap / "simple" consumer mains appliances, including non-"smart" microwaves, ovens, alarm clocks, etc. still use mains frequency as their time reference.
Due to the growing complexity of power grids and in Europe, international power-grid politics and infighting, the grid frequency is becoming less stable and you see these devices fluctuate badly more often than they used to. https://hackaday.com/2018/03/09/europe-loses-six-minutes-due...
I find this incredibly hard to believe. Crystals are incredibly cheap and waaaaaay more accurate than anything that the grid does.
If you're not an actual motor, sensing the grid is both an engineering challenge and a non-trivial expense.
The grid has poor short-term performance, but the long-term frequency is averaged out to be exactly 50/60Hz.
Turns out it had a button combo for “switch between 50Hz and 60Hz mode” that was similar to its combo for (what I thought I was setting) “switch between 12- and 24-hour mode”. (I think the 12/24 switch was “hold the hour button down while plugging in” and the 50/60 switch was “hold both buttons down while plugging in”.)
Some systems still use grid frequency for timekeeping.
If you own a mechanical rotary timeswitch, it's got a synchronous motor spinning 50 or 60 times a second, then a series of gears, gearing it down to 1 rotation per day.
https://www.theguardian.com/world/2018/mar/08/european-clock...
Very, very well done
