Audio detection in Axis cameras is used to detect changes in decibel levels, which can indicate unusual or noteworthy events such as alarms, breaking glass, or raised voices. This functionality does not necessarily require a built-in microphone; it can also work with external microphones. The primary function is to trigger alerts or recordings based on significant changes in the audio environment. Axis Network Video documentation outlines the use of audio detection for enhancing security by monitoring for specific sound patterns or levels.