system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why do phones not pick up their own noise when on speakerphone?

This isn't an issue any more. But I remember old cell phones from when I was younger, the microphones would pick up noise from it's own speaker and make the call echo. What mechanism is in place that prevents this nowadays?
gpt
Long story short the phone knows what is coming out of the phone and ignores it when recording sound

Basically it still does pick it up on the microphone but the phone knows that it is an echo so it cuts it out of the playback.