The Ubertooth One is an open source 2.4 GHz device suitable for Bluetooth experimentation. Based on the powerful LPC175x ARM Cortex-M3 microcontroller with full-speed USB 2.0, the Ubertooth One is a great way to develop custom Class 1 comparable Bluetooth devices. The entire board is onlytwo and a half inches long with a USB-A connector at one end and an RP-SMA connector at the other.
One thing that sets the Ubertooth apart from other Bluetooth development platforms and Software Defined Radios (SDR) is that it's capable of not only sending and receiving 2.4 GHz signals, but can also operate in monitor mode, monitoring Bluetooth traffic in real-time. This operating mode has been present in low-cost WiFi modules for years and has found myriad uses in research, development and security auditing but no such solution existed for the Bluetooth standard until now. Also, because it's a fully open-source platform (software and hardware), the schematics and code are readily available for all of your hacking needs.