Airport security screening relies heavily on metal detection devices; screening for explosives in liquids has proved to be elusive—most liquids are simply confiscated. While researching degenerative diseases such as Parkinson’s and cancer, UC Berkeley chemist Christopher Chang developed a chemical sensor that identifies hydrogen peroxide—which living cells excrete when stressed. Hydrogen peroxide is also the main ingredient in a popular homemade explosive. Chang quickly devised a plan to convert his “peroxysensor” for use in anti-terrorism security screening.