This patch uses nanomagnets to detect muscle movement through the skin

Using nanomagnets composites and conductive yarn, scientists have invented a smart textile that can sense and measure body movements -- from muscles flexing to veins pulsing. The device is self-powered, stretchy, durable, waterproof, and can be made with a sewing machine for a few dollars. It may one day aid clinicians in assessing muscle injuries and support patients' recovery.