@fakeirish @Liquidxlax : in the novel only like 2 nations have the tech to detect all gates on an area (and Korea is not one, but Jin-Woo will be given access to the tech after providing certain services to a nation holding the tech, it is satalite based BTW)
But ya, there are gates that erupt all the time, and one has been seen before.
Having tech to detect gates would be a
plot hole considering that we have seen the results of a low rant gate opening/outbreak already in the story back when Jin-woo was leaving (I think his first) private/instanced/etc dungeon.
Though even without the tech, measures to check for a gate would become standard practice but it would not be a perfect system. Though normal maintenance and custodial/janitorial duties should detect most gates in cities.