Yogesh Gianchandani, a researcher at the University of Michigan, has developed a tiny wireless Geiger counter that can be used in a network to cover large areas like stadiums or malls and distinguish between harmful and non harmful sources of radiation. And since they're so small (about the size of a postage stamp, as you can see), they can be placed in inconspicous areas, which is both more feasible and much less likely to freak people out than a bunch of dudes in white lab coats walking around with ticking boxes. While development of the device seems to be well on track, it's probably still a ways off from going into production, which means you'll need to look to other solutions if you want to be prepared for when the Commies finally drop the big one.

The Giovannoni TimeSphere projecting alarm clock