In the 80s my uncle had digital clocks that used an antenna to tune into the atomic clock time signal that (was/is?) broadcast nationwide. I've long wished that it was incorporated into stoves, microwaves, essentially everything that isn't an internet device (yet... sigh)

Sadly I think the actual antenna and hardware were relatively large since it's a long wave signal, but maybe with SDR it'll all fit on the head of a pin these days.