In this video, a materials science laboratory at Harvard University is filled with music (the “Morning” prelude from Peer Gynt) played on a transparent ionic speaker. The speaker consists of a thin sheet of rubber sandwiched between two layers of a saltwater gel. A high-voltage signal runs across the surfaces and through the layers forces the rubber to rapidly contract and vibrate, producing sounds that span the entire audible spectrum, 20 hertz to 20 kilohertz. This device represents the first demonstration that electrical charges carried by ions, rather than electrons, can be put to meaningful use in fast-moving, high-voltage devices. "You can integrate it anywhere you would need a soft, transparent layer that deforms in response to electrical stimuli - for example, on the screen of a TV, laptop, or smartphone to generate sound or provide localized haptic feedback - and people are even thinking about smart windows," says Harvard postdoctoral fellow Christoph Keplinger.