It's a wireless "piano" and tunes maker for your phone via your burger tray. That's a lot of joy being delivered from an unexpected source.
What a killer addition to your burger visit. Chances are that if you're not making the beats your dinning neighbor has figured it out and is jamming out. I'd return for another Big Mac with a side of loops and tunes.
I wonder how many of these they started with vs. ended with. Kleptoville? What's the unit cost? Let's get a few more of these made. I want to try! Link.