Following the events which took place on September 11, 2001, and the anthrax attacks which occurred after that date, US authorities became concerned with the idea that an assault with chemical or biological weapons could take place on American territory or in American ships or planes. A worrisome model for such an assault was the 1995 terrorist attack carried out on the Tokyo, Japan, subway system, using sarin gas. This paper discusses the possible ways to do in order to prevent casualties if such an attack took place. One idea was to use sensors that, like smoke detectors, would warn of impending danger. That concept became the foundation of the "detect to warn" strategy that served as the basis of efforts to protect public places. With a close examination of this strategy, this paper reveals that there are three major flaws that reduce the value of this approach and risk creating a false sense of security.