In 2012 the engineers working on Google's self-driving car realized they had a problem. Early testers had agreed to always watch the road in case of emergencies, but many didn't--and it put them at serious risk. This is what's known as the handoff problem: how to alert and engage the distracted human when the computer falters. Bypass the issue by building a vehicle that operates entirely on its own.

ASK ALEXA ABOUT the weather, and it'll tell you it's sunny and 75 in a pleasant monotone. Prompt it to tell you a joke, and it'll offer a pun in its signature staccato. Suggest that it sing a song, and it'll belt out an auto-tuned country ballad. Amazon's virtual assistant boasts a number of clever, humanlike abilities--but, as its voice betrays, Alexa is still just a robot.