In Kyllo vs. United States, the Supreme Court ruled that the use of sensory-enhancing technology to see through traditional privacy barriers constituted an illegal search in violation of the Constitution’s Fourth Amendment protections. This article examines the history of Fourth Amendment applications involving the use of technology by government officials. The authors discuss the implications of Kyllo in light of emerging technologies available to the government as a means of gathering incriminating evidence against persons either engaging or conspiring to engage in criminal behavior. Ultimately, they argue that the Kyllo standard for the application of sensory-enhancing technology has important implications for the future of law enforcement and the ongoing fight against international terrorism.