What happens when the robots sound too much like humans?

Artificial intelligence has a new challenge: Whether and how to alert people who may not know they’re talking to a robot.

On Tuesday, Google showed off an AI assistant that makes convincingly human-sounding phone calls, at least in its prerecorded demonstration. But the real people in those calls didn’t seem to be aware they were talking to a machine.

Google says its digital voice assistant can make some of our most tedious calls, such as reservation for dinner or a haircut. The AI speaks with pauses and “ums” and “mmm-hmms” to sound more human.

But it may not be fair — or even legal — to trick the hairstylists and restaurant employees answering the calls.

Google calls the new service, known as Duplex, an experiment.