The key is the bone conduction speakers.

Customers who aren't fond of delicate ear buds or bulky earphones can consider the Zungle Panther, a pair of sunglasses that transmits music via built-in bone conduction speakers. Tom's Guide reports that the sunglasses, which resemble Ray-Ban Wayfarers, are a Kickstarter project for Los Angeles-based Zungle and are expected to ship in February 2017. The Bluetooth-compatible frames feature speakers that sit behind the ears, meaning wearers can still hear sounds from sources in the world around them.

Read more at Tom's Guide