Drove back and forth from Bangkok to Hua Hin this week on the main road (35 / Rama III, and then 4 south).
There was one check-point just after the airport in Hua Hin, but no cars were stopped.
Hua Hin looks a like a ghost town.
You can check the latest provincial measures here:
https://www.tatnews.org/2021/01/tat-update-summary-of-provincial-covid-19-control-measures-as-of-6-january-2021/
I found this for Krabi:
+ Arrivals from the highly controlled areas are required to register their entry online or report to the local administration and enter a 14-day local quarantine.
Not sure though whether the policy is really implemented, and what it looks like on the ground .
Some of my Thai family members take these announcements really serious. But I wonder what the enforcement/implem