Here are two articles, here and here, both from MIT Technology Review, describing advances in the technology of explosive detection, some of which have been used in Iraq to hunt down the IED makers. The older technology is able to detect TNT even when packed inside closed containers. Newer methods under development promise to extend that capability to detect RDX and PETN.
Improvements in detector technology, combined with new tactics, made it possible for antisubmarine forces inflict increasingly heavy casualties on a hidden enemy while in preparation and transit. While the analogy is not exact, I mention it to underscore the far from unimportant role improved sensors have in fighting against an enemy whose tactics have been optimized to hide inside a "sea of people" full of its own ambient noise but within which lurks a deadly threat.