This is a simple swift app that demonstrates very basic bi-directional communication with an Arduino via bluetooth. It is designed to work out-of-the-box with an Arduino 101 running the ButtonLED example project.
You can read more about this project on my medium post.
Simply connect a push button to pin 4 on your Arduino 101 an upload the ButtonLED sketch to it. While the Arduino is running, launch the HelloBluetooth iOS app on a device. You can then play with the push button or the button in the iOS app.