Help Sensor used for gestures

[devswap]

I wanted to know which sensor is used to detect gestures on the S4. I thought initially that it must be the camera but then I figured to keep this running constantly would be a big battery drain. Can anyone advise which sensor is used and if you know roughly how much it drains the battery

Thanks

 

[El Presidente]

Looks like there's a special sensor for them: How do I use Air Gestures to control my Samsung Galaxy S