The Apple Watch is not a medical device. Sure, it can keep an eye on large changes in your heart rate, making it reasonably good at telling you how long you worked out for. But anything more than that is a bit outside its capabilities.
Robots clean rivers and sort waste, monitor ecosystems, and inspect renewable-energy infrastructure. But even the greenest robot has an environmental footprint.
EPFL engineers have designed acoustic cavities that convert sound waves into thrust, propelling small robots and ultralight aerial vehicles without on-board actuators or electronics.