Charles Stross has a book series about a family of people that can step between different timelines of alternate Earth's that explores this a little. **SPOILER

Charles Stross has a book series about a family of people that can step between different timelines of alternate Earth's that explores this a little. **SPOILERS** Once the US that's basically our world discovers the existence of "world walkers" when they nuke the Whitehouse, it quickly steps into an authoritarian surveillance hellstate capable of realtime surveiling the population around the country to the point where they can track people entering their timeline because they were on camera exiting a building they were never recorded entering, or were flagged buying a plane/bus ticket from a city they shouldn't have been in according to previous records, or in one case for leaving a coffee shop with a noticeably empty backpack when she'd entered the shop with it completely full, having passed the contents to a world walker she was meeting. That irregularity automatically flagged everyone entering/leaving that building for review in their system and they backtracked all of these people through their paths that day until finding the gap where he'd stepped through to their world. That all happened in a matter of minutes and then quickly homed in on him. Anyhow,it goes into detail about the lengths they go to to avoid detection by these systems and honestly didn't strike me at as all farfetched. The technology and capacity exists and it's a concentrated effort on part of the government is all it would take to implement it.