Searchers have time and tide against them as they narrow the hunt for a missing Malaysian Airlines jet using final "pings" from flight recorders soon to fall silent.
Finding the boxes will be just the start of a challenge to pluck wreckage from the ocean that may stretch technology to its limits.
For the second time since Flight MH370 disappeared after leaving Kuala Lumpur on March 8, experts are having to rely on metronomic whispers from the plane's electronic systems to try to track it down.
It was satellite pings that led searchers on the path south to the Indian Ocean where an Australian ship picked up possible pings from the recorders on April 5.
Now, they are searching blindfolded in one of the most murky, noisy and isolated spots on Earth, three miles under water where the jet is assumed to have crashed with 227 passengers and 12 crew on board.
On Wednesday, Australian officials said two new ping signals had been detected the previous day. The recorders' batteries are now about two days past their regular lifespan.
Finding the recorders won't just help locate the jet. They record cockpit data that could help explain what happened to the plane and why it flew thousands of kilometres off its Kuala Lumpur-to-Beijing route.
"Now that 30 days have passed we are in bonus time," said Anish Patel, head of Florida-based pinger maker Dukane Seacom. "The units are certified to last 30 days but there is a small design margin ... (of) a few extra days of power."
The first priority for search crews will be to cling onto the electronic signals long enough to narrow the area for more thorough sonar research.
Australian ship Ocean Shield is using a 'Towed Pinger Locator' sent by the US Navy - described by France as the most capable of its kind after it was used in the ultimately successful search for an Air France jet that crashed in the Atlantic in 2009.
"The problem is not localising it, the problem is finding where to look in the first place," said Mike Davis-Marks, a former submarine commander in Britain's Royal Navy.
It's a slow and exhausting process.
Operators must separate a ping lasting just 9.3 milliseconds - a tenth of the blink of a human eye - and repeated every 1.08 seconds from the natural cacophony of the ocean, as well as disturbances from other search vessels.
"The ocean is a noisy place," said Davis-Marks, former commander of a sister vessel to British hunter-killer submarine HMS Tireless which has been dispatched to assist in the search. "There is noise from everything, whether it's the ambient noise of the weather at the surface, or marine life like whales or the snapping noise of shrimps, not to mention other sea transport and low-flying aircraft."