I made a little gadget that detects nearby iBeacons (they're a sort of "indoor position system"). It's a Raspberry Pi with an LCD/keypad plate and a Bluetooth dongle running a Node application. Here's a video:

The little plastic rocks are iBeacons from Estimote that I tested against. The screen displays the UUID for detected beacons and their RSSI (signal strength, higher means closer, note numbers are negative). The keypad cycles through nearby beacons in the order in which they were discovered. As I move the Estimotes (UUIDs labelled) around in the video, the RSSI value changes as expected.

Code is here. More detailed post to come.