Bluetooth Enabled Luggage Tags by Phil Windley:
This is just a concept, mind you, but its a good one. In response to an industrial design contest at IDFuel, Nathan Lynch and Lea Miller had proposed a Bluetooth enabled luggage tag that lights up when the cell phone its paired with is nearby and sends the phone a message. The tag also contains contact information for the owner of the luggage. Essentially, this is presence for physical objects and there are all sorts of applications that spring to mind.