Old school electric clocks used to (still?) keep time with the grid frequency. Guaranteed to always have N cycles per day. So if things are gradually failing, you might be able to see your clock keeping worse time.
That's not going to work, because the clock will mainly be showing phase drift.
Having the grid operate at 49.99Hz instead of a perfect 50.00Hz for a day will make your clock lose 17 seconds, but it's completely harmless. That's normal regulation, not a gradual failure. The grid chooses to compensate for that by running at 50.01Hz for a day, but that's solely for the benefit of those people with old-school clocks - the grid itself couldn't care less.
A failure means the frequency drops from 50.23Hz to 48.03Hz, probably within a single second. You'd notice as your clock stops ticking due to the resulting power outage.
Yes, it's not that hard. There's smart meters and plugs that have frequency measurement built in.
You can even do it with an audio cable: https://halcy.de/blog/2025/02/09/measuring-power-network-fre...