From Ed Gottsman: The Lawrence Livermore National Laboratory, with funding from the US Department of Homeland Security, has developed a "smart" cell phone that sits on a security officer's hip and continuously transmits radiation readings to a central server. These readings are used to develop a map of existing radiation sources, which in turn is used to detect new, illicit sources of radiation, should they appear.
I blog a lot about sensors, but these are the most interesting I've ever seen--not because of what they sense (geiger counters are old news), but because of their packaging. Since they're cell phones (albeit probably expensive ones), there's no reason their use couldn't expand beyond security officers to, let's say, the general public. It's not hard to imagine cell phone companies offering the Patriotic Option, a global positioning system-enabled phone that automatically detects radiation, illicit chemicals and mimes (I hate mimes) and alerts the appropriate authorities for swift and efficient intervention. Leave the phone peeking out of your breast pocket with its camera on and a DHS image processing program could even examine the video feed for the faces of wanted suspects. You could argue that all of this would constitute a gross government invasion of your privacy--but security and privacy have always been at odds. At least this way you get to decide whether to expose your activities for the greater good.