As an undergraduate in Mumbai, India, Saad Bhamla wanted to do something nice for his maternal grandparents: Buy them a pair of hearing aids. But the prices were shockingly high—and far beyond his means. Now, 15 years later, the bioengineer has invented a device to help grandparents across the globe: a do-it-yourself hearing aid made from inexpensive, easy-to-find parts. The no-frills device, described in a new study, could help restore hearing to millions suffering from age-related hearing loss—for less than the price of a bottle of water.