To put it simple, Xmart Volume utilizes the built-in mic of your Mac or iSight.

It actively “listen” to the environment sound level. It turns down your headphone volume when it detects any sound which is louder than the background noise.

Here are some situations you might find Xmart Volume useful:

Xmart Volume turns down your headphone volume when someone (e.g. your colleague or boss...) talks to you.

Although not guaranteed, Xmart Volume reduces your chance of missing important announcement when you are enjoying a movie or iTune on your MacBooks while waiting for a flight in airport.