AS CHILDREN everywhere are delighted to learn in science class, sound can shatter glass. Might it also be possible, then, to use acoustic waves to disrupt the electromechanical sensors that drones require to fly? To find out, four engineering students at the University of Toronto repurposed small car speakers to cobble together a contraption “for blasting a drone with sound”, as one of them, Michael Acquaviva, puts it. It worked in early tests, though only at close range. Drones 50cm away wobbled. At 25cm, they crashed.