With President Obama in town last Wednesday, things were busy for the New York Police Department’s Harbor Unit. Federal security agents were disseminating lists of city locations that had to be swept for bombs, cleared and guarded.

That meant that coastal areas near touchdown points for Marine One, the presidential helicopter, demanded extra inspection. Police divers splashed down to scrutinize underwater sections of piers and seawalls for improvised explosive devices. Radiological sweeps were done. Each of the bridges spanning waters that Mr. Obama’s motorcade might cross got a top-to-bottom going over.

NEW YORK (AP) — The New York Police Department is testing ground-breaking counterterror technology expected to dramatically increase its ability to detect and thwart a potential radiation attack, officials said Thursday.

The technology will allow a command center in lower Manhattan to monitor 2,000 mobile radiation detectors carried by officers each day around the city. The detectors will send a wireless, real-time alert if there’s a reading signaling a dirty bomb threat.

The system already is being tested under the watch of federal authorities in hopes it can be perfected and used elsewhere.