Audio Control
If any audio on a web page plays automatically for more than 3 seconds, either a mechanism is available to pause or stop the audio, or a mechanism is available to control audio volume independently from the overall system volume level.
In plain language
If a page automatically plays sound for more than 3 seconds, there must be an easy way to pause or stop it, or to control its volume separately from the device's overall volume.
Why it matters
Unexpected audio can drown out screen readers (making the site unusable for blind users), startle people, or make a page unusable in quiet places. Without an easy way to stop it, people are stuck fighting the sound.
In practice
Fails this criterion
A page auto-plays background music for over 3 seconds with no visible pause or stop button anywhere.
Meets this criterion
A clearly labeled "Pause audio" control appears near the top of the page as soon as the audio starts, letting anyone stop it immediately.
Test it yourself
Load the page and listen for any audio that starts automatically. If it lasts more than 3 seconds, look for a pause/stop control or independent volume control. If there isn't one, the criterion is failing.