This month's Reason contains an excellent article entitled, "The Pinpoint Search: How super-accurate surveillance technology threatens our privacy." The author, Julian Sanchez, notes: "A new wave of advanced surveillance tools is capable of detecting not just drugs but weapons, explosives, and illicit computer files, potentially flying under the Fourth Amendment’s radar all the while."
Sanchez asks, for example:
A handheld scanner picks up stray particles of cocaine on a car during a routine traffic stop. Is that a search? A high-tech camera detects the gun one pedestrian is carrying under his jacket. Is that a search? A forensic analyst finds a single image of child pornography on a computer server containing thousands of files owned by hundreds of users, without ever seeing any other private information. Is that a search?
The discussion of pinpoint searches as a means of combating terrorist activity is especially interesting. The entire article, though, is worth reading.