The microKEY-37 AIR from Korg is a slim MIDI controller with a pitch wheel, a modulation wheel, and a set of 37 velocity-sensitive Natural Touch mini-keys. If you wish, you can bus-power this unit via the USB port, but the microKEY Air also features Bluetooth capabilities, allowing you to connect wirelessly to Mac and iOS devices. Hooked up in such a fashion, the keyboard can last up to 30 hours on two AA batteries (alkaline are recommended).