Ubertooth One is the perfect tool to perform Bluetooth or BLE (Bluetooth Low Energy) sniffing. Developed by Michael Ossman of GreatScottGadgets, this tool has been used a number of times by us at Attify during our pentesting engagements.
You can sniff traffic - actively and passively, pipe it to wireshark directly, identify interesting values from the live capture to take control of an IoT device and lot more.
Definitely worth buying if you're into IoT security research and pentesting. Read how to use it at Attify Blog .