Scientists have created a keypad lock a single molecule in size. This lock only activates when exposed to the correct password, a sequence of chemicals and light. Researchers suggest their device could in the future lead to a new level of safeguards for secret information. This lock might also serve to recognize when certain sequences of chemicals are released in the body--for instance, after exposure to Sarin or another deadly chemical or biological weapon. Organic chemist Abraham Shanzer and his colleagues at the Weizmann Institute of Science in Rehovat, Israel, began with a molecule named FLIP. At its core is...