Bluetooth 4.0 (Smart, Low-Energy) modules are supported on both iOS and Android. Bluetooth 2.0 (Classic, Serial Port Profile) modules are supported only on Android.
When adding new hardware project, select Bluetooth or BLE connection method
Add "BLE" (for BTLE) or "Bluetooth" (for SPP) widget
In widget settings, click Connect button. It should say "connected"
Run your project
Home-screen widgets are not usable for Bluetooth projects
Some widgets are not working with Bluetooth: RTC (will be enabled later), History Graph, Bridge, Eventor, WebHook, Twitter, Notification, Email
If "BLE" or "Bluetooth" widgets are not shown, it means your smartphone doesn't support it (be sure to enable Bluetooth and Location Services).
If it doesn't get connected:
Restart your phone and retry
Try using original examples of your hardware/library providers - maybe the problem is in hardware/wiring