Meet the Universal Foldable Keyboard: a compact keyboard that lets you type on your iOS/Android device more easily. It connects to your smart gadgets using Bluetooth 4.0 technology. The rechargeable battery lasts you up to 3 months. You can pair the keyboard with two devices and witch between them with a single touch.
The Universal Foldable Keyboard from Microsoft is compatible with Windows devices as well. Sets you back under $100 when it ships.