Transcript for Last-Ditch Effort in Flight 370 Search as Black Box Batteries Run Low
To the latest on the could be founding search for flight 370 after almost four weeks nothing has been found. The lien's black boxes are ticking down. Only days left before the batteries go dead and David Kerley has been tracking this. Searchers using a technology which may be the last best hope. This is the news this morning. Two of those towed ping locators are being dragged through the water listening for the last possible pings or ticks from those pingers on the black boxes. How do they know where to tow these high-tech listening devices without finding debris? Well, they really don't. The head of the search says they're taking their best guess. A 150-mile area inside one of these air search area, 150 miles, very small. The rush is on because the 30 days on those batteries hits on Sunday, George. Time is ticking. And is there any give on that deadline at all? Yeah, it's -- the batteries are guaranteed to last for 30 days then they start to fade kind of like a flashlight when the batteries go. The Nall is going to dim so they'll have been to be even closer and have to be within a mile or two at this point. They'll have to be closer after that 30-day mark in as you say they are just guessing. Okay, David, thanks very much.
This transcript has been automatically generated and may not be 100% accurate.