BlueTooth Pairing and Discovery Extension ($) - vknow360
BluetoothLE extension 20200828 released - ewpatton
Bluetooth error codes
Documentation for the BluetootClient component (for BT<4) can be found here: http://ai2.appinventor.mit.edu/reference/components/connectivity.html#BluetoothClient
MIT provides an extension to use the Bluetooth Low Energy (BLE). Since June 19, 2017 the support for BLE has been greatly expanded and improved. A starting point for finding documentation, tutorials and more is the: App Inventor IOT site
Which Bluetooth protocols are supported? (discussion)