How do you see in the dark or see what can't be seen? Some tools identified here:
The mission of the U.S. Department of Homeland Security (DHS) and the U.S. military is, in part, to ensure the protection, safety, and security of the nation and its citizens. Science and technology are playing an ever increasing role in this mission. In fact, the Directorate for Science and Technology, the primary research-and-development arm of DHS, is working in partnership with private businesses, national laboratories, universities, domestic and foreign government agencies, and the military to drive the development and use of high-tech solutions in support of securing the nation. Together, the homeland security and military communities are making significant strides in technology, particularly in the vital areas of intelligence and surveillance.One example here.
UPDATE: On the other hand, these tools have to be part of a larger effort, not the sole line of defense.