Here is a pretty good primer on the fundamentals of Bluetooth.
Bluetooth can be intercepted with a couple of Bluetooth USB dongles and software such as GATTacker or BtleJuice, as detailed in Melamed, An active man-in-the-middle attack on bluetooth smart devices, 2018 and Melamed, Hack-a-ble: Hacking BLE Smart Devices, 2017. We can also use the Ubertooth One to intercept Bluetooth signals from your target.
Bluetooth comes in two flavors, Bluetooth Classic and Bluetooth Low Energy (BLE). Here is a pretty good video introduction to BLE.
Some interesting new vulnerabilities were discovered in February 2020. More information here: https://asset-group.github.io/disclosures/sweyntooth/