A U.S. Army ranger is on a battlefield in a country known to be making chemical weapons. Through his binoculars, he spots a cloud of smoke a mile away. Does it contain lethal gas? At the moment, there is no easy way to know. But researchers at Sandia National Laboratories and MIT are working on a dime-sized sensor that could be built into binoculars or telescopes to spot toxic gases before they do any damage.

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