Amazon Echo and Alexa
Amazon released a speaker that listens to the room continuously and answers when addressed, making voice the primary interface rather than an addition.
Why it matters
A far-field microphone in a living room created both a new mode of interaction and a new argument about privacy.
The technical difficulty was not recognition but hearing: a circular array of seven microphones with beamforming, noise reduction and echo cancellation to pick a voice out from across the room. The device opened skills to third-party developers from 2015, and by its fifth anniversary Amazon counted more than a hundred thousand. It also began a long public argument about devices that are always listening.