DORA is a device that can obtain RSSI info from certain Spektrum Rx units and OSD this info back to your FPV station. To my knowledge this is the only device out there that can do this. http://www.ebay.com/itm/DORA-translates-Spektrum-DSMX-receiver-output-into-RSSI-signal-for-OSD-FPV-/321109017572?pt=US_Radio_Control_Control_Line&hash=item4ac396c3e4
Further reading, looks like this is an add on to your existing OSD? http://fpvlab.com/forums/showthread.php?7168-RSSI-from-Spektrum-receivers
Interesting product. Funny how it counts down to zero when the radio is switched off. Like the last radio waves are still coming in until they run out.