This anti-terrorism concept from researchers at Purdue University puts together miniature radiation counters built right into cellphones across the US. Each solid-state sensor would be able to sniff out radioactive sources from up to 15 feet, and then would send in the location to Homeland Security, the FBI and Jack Bauer, resulting in huge dirty-bomb surveillance system. Sounds like 24 meets Big Brother in 1984, but it is a pretty clever system and apparently it works right now.
Professors Ephraim Fischbach and Jere Jenkins suggest that the electronics could filter out false alarms from medical radiation sources and radioactive potassium in bananas (wait, bananas are radioactive? Who knew!) and the sensors themselves would add little weight to a cellphone or laptop. The system could track the progress of suspicious radiation sources (like a badly-shielded suitcase bomb) across the country, and even act as an alert system for radiation leaks from the legitimate nuclear industry. It's also been tested on campus, using a very weak radioactive source, demonstrating that the technology already exists.
If you didn't mind doing a little cloak-and-dagger work for the Government as you walked around with your phone in your pocket, then this sounds like it could be a pretty effective anti-terror weapon. [Purdue press release via TG Daily]