A term I've seen thrown around is "good old-fashioned police work" and to me the clear distinction is that it can't be done en masse - a real human police officer had to spend time tracking down each known suspect. E.g. clipping a pen register onto someone's telephone wires, tailing someone, asking the hotel clerk if he's been there, unlocking someone's phone to read their messages, and even watching footage on airgapped CCTV systems are all tasks that can be done one-at-a-time and require human power proportional to how much of them you do. This forces the state to only use them on actual suspects instead of using them on everyone, but still doesn't prevent the state from catching criminals.