There was a CNN report this evening (26th May) quoting the Egyptians as saying that some sort of beacon has been detected, enabling the search area to be shrunk to a few km2.
According to the reporter, the Egyptians are attributing this information to Airbus, yet the beacon in question only has a transmission life of 2 days, suggesting that the information is a few days old. One set of specs on the Technical forum seems to indicate that these beacons transmit for much longer than two days. I was perplexed by the CNN report -- thanks to the Technical Forum I am at least perplexed at a slightly more informed level.