The days of wearing headphones for listening could soon be gone, because Amazon’s planned smart glasses are set to use bone conduction to transmit sound through your skull, according to a report.

Amazon‘s Alexa assistant is set to power its smart glasses, the FT reported, and wearers will be able to hear Alexa’s responses to questions via their frames, transmitted through people’s skulls.

Those nearby will not be able to hear responses from the smart assistant, only the glasses wearer.

Devices that use bone conduction have been around for a while, such as Audio Bone headphones, which don’t actually go in a wearer’s ears, but sit in front of them held in place by a band behind the head.

It’s also the technology behind Glass, the smart glasses launched by Google parent company Alphabet as a consumer product in 2012, now used by businesses in manufacturing and logistics, for example.

Google and Amazon both want to be major players in digital assistants, smart technology that is powered by a person’s voice. Amazon’s Alexa could be worth $10 billion in revenue by 2020 according to RBC Capital Markets.

Amazon’s Alexa digital assistant will be available “hands free” in its new Fire HD 10 tablet, it announced Tuesday, while Chinese technology company Qihan launched a $2,800 robot powered by Alexa in August, named the Sanbot Nano.

Amazon did not return CNBC’s request for comment.