What you can’t smell can hurt you. That’s the idea behind electronic noses—sensors that detect harmful gases, such as ammonia or carbon monoxide, at much lower levels than the human nose can. Commercial e-noses are used in the food industry, in hospitals, and on NASA space shuttles, but they have generally been too expensive for consumer use. But Vivek Subramanian, an associate professor of electrical engineering at UC Berkeley, is building cheap e-noses that can be printed quickly and cheaply with plastic “ink.”