SILENTLY think of a question and I will answer it. That might sound like a magic trick, but it is the promise of AlterEgo, a headset that lets you speak to a computer without ever uttering a sound. It’s not quite a mind reader , but it is close.

The device brings us a step closer to a world where we can interact seamlessly with machines using only our thoughts. AlterEgo’s creators believe that rather than embarrassingly saying things like “OK Google” or “Hey Siri” and then …