We love the slim, sleek design of portable electronics these days, like the iPhone. One of the only reasons phones and MP3 players haven’t shrunk beyond human visibility is basically because, well, the buttons need to go somewhere.

As mobile devices get teenier and tinier, manufactures have been trying to fit buttons and controls onto the diminishing surface area. But with a brand new technology created by researchers at Carnegie Mellon and Microsoft called Skinput, this may never be a problem again.

Skinput is a bio-acoustic sensing device that uses your own skin (your arms and fingers) as a space for buttons and controls. The user wears an armband with a small projector that displays menu options on the arm. When the users touches a button, an acoustic sensor analyzes distinct sounds made on the surface of skin related to specific bone density, joints and tissue. That information is delivered through a Bluetooth device back to the device to determine what button has been pressed.

So if you thought people looked funny walking down the street talking into invisible earpieces, imagine people on the subway tapping their own fingers to change a song on their iPod.

Watch the video to see Skinput in action: