The JamStik can do that!
What's a JamStik? The JamStik is a portable digital guitar that connects to your iPad or iPhone! We use light to scan your fingers as
you press REAL STRINGS to REAL FRETS and use REAL PICKING technique to
play, then send that information over to your device in real time to
take some of the frustration out of learning to play and put some fun
back in!
Aside from being called "the coolest thing at CES 2013" and heralded as one of PopSci.com's
Top 10 Inventions of 2013, the JamStik also works with a whole world of
iOS CoreMIDI apps that are already available in the iTunes App Store.
Awesome apps like Apple's GarageBand, Moog's Animoog, Korg's iPolysix
& iMS-20, Arctic Synth, Sunrizer, the list goes on and on. If it
does CoreMIDI, JamStik can control it!