How Do Smartphones Know When You're Talking to Someone Else?

Smartphones listen for sound and use small sensors to tell the difference between your voice and someone else's. It’s like having a tiny detective in your phone who can hear when you're talking or when someone else is on the other end of a call. The phone uses math to figure out which voice belongs to whom, it’s kind of like how you know which friend is speaking at a party just by listening.