Racing to find survivors buried in the rubble of collapsed buildings before it's too late, specialized search and rescue teams know their only indication that a victim is trapped may be a faint scratching or a weakened cry for help.
It's a difficult task in a densely populated city like Port-au-Prince, where the city's approximately 3 million residents have flooded the crumbled streets afraid to seek shelter because of continuing aftershocks.
Yet when the calls go out, the silence is largely granted even by those who are the most panicked.
"They know the rescuers are using this to save people," said Battalion Chief Bob Zoldos of the Fairfax County Fire and Rescue unit, one of the first to reach Haiti.
And it's not as simple as hushing bystanders. Simple background noise such as the sound of running water or rescue crews working to free a victim five buildings away can throw off a team's search, wasting valuable time.
While on his first mission to the 1998 embassy boming in Kenya, "we would actually announce to everyone there that we need silence and the amazing thing was that the chaos actually did stop," Zoldos said.
The next year, when he was in Turkey after the massive earthquake that killed more than 18,000 people, victims did the same.
"That was more difficult, but still you could get more people in the area to quiet down," he said. "It can be done."
And in a place like Haiti, where citizens are desperate to find their loved ones, Zoldos said he expects similar cooperation.
Zoldos' colleagues with the Virginia Task Force 1 are already at work in Haiti -- 72 rescuers were dispatched Wednesday along with six dogs. Zoldos will lead the second team being prepped for deployment.
The difficulty with finding survivors trapped in what's left of the buildings is knowing whether anyone is even in there. Tapping noises could be someone's cry for help or the sounds of a weakened building settling.
The dogs are brought in immediately, Zoldos said, because their ability to sniff out a survivor and detect low level sounds are far superior to anything their human team members could do.
As their handlers listen for the dog's bark, teams pull out seismic listening devices that will give rescuers rough coordinates of where the survivor's are in the rubble.
Roughly the size of a soda can, the orange devices are reliable at picking up vibration, Zoldos said, but can easily be fooled by outside noise.
"When you're looking for scratching or something like that or someone tapping it is very hard to distinguish," he said.
Now nearly 48 hours into the recovery effort, Zoldos said, rescuers are eager to get those people out.
"There's been rescues all the way to day nine, 10 and 11 depending on the injury of the person, the environment, the exposure -- all that plays into their suvivablility," he said. "If there's any chances people are there, we want to search it."
Right now crews in Haiti are in "blitz mode," working until they can't physically go any longer. In Turkey, he said, his team went 56 hours without stopping.