How do secret agencies, law enforcement agencies, army, etc intercept suspicious talks of terrorists on borders? What tools do they use?
Quick answer: They use technology, spying and government games
They use build-in tools that take advantage of encryption system’s vulnerabilities,they have gadgets that cost millions of dollars and there is no way to submit these tools and gadgets in the public. (This is very obvious)
But this question cannot be answered in just 2 lines
They have access to cameras, mobile agencies, ISP’s data, satellites, and what I mentioned above.So they have eyes and ears everywhere.
But you may think that agencies etc know who are the terrorists from the beginning,but that’s not true.
They are spying every place in the suspicious areas, sometimes for years.For example Bin Laden’s case.
They where just 60% - 80% sure that Osama was in the house were he was,but not because of calls,but for the people’s movements in this area.
So the answer concludes real life spying,cyber security,government games etc.
I recommend you to see the series “The Spy”,the movie “The big hack” and check spies’ training etc.