Korea is a surveillance society. Business make you scan a QR code that you are required to have on your phone, or at a minimum fill in a sign in sheet that includes your phone number. If required to quarantine, you have to install a location monitoring app that tracks your GPS position and if you go more than 25 meters from your required and registered quarantine location it sends a message to the government immediately. More than three violations and they put an ankle GPS tracker on you. Still violate? They either deport you or take you to jail, along with a several thousand dollar fine. They are SERIOUS about this too, it is not an idle threat, they actually do this. If you "cheat" but leaving your phone behind, their app software detects that too,: if a phone does not make some small movement every 30 minutes they call you, no answer, you're busted. While their system is not 100% perfect, it stops on the order of 90% of the quarantine cheaters in a society that is fundamentally not inclined to cheat anyway.
CCTV cameras everywhere, all feeding to the government. The have, and use, best of class facial recognition software for contact tracing. Masks are no problem for this software, by the way.
Korea has seen only marginal success in managing 'rona transmission with all this. Hmmmm.