Yesenia D'Alessandro loaded a GPS tracking app on her cellphone and trudged into a remote Hawaii forest, joining more than 100 other volunteers looking for a missing hiker.
She climbed through muddy ravines, crossed streams and faced steep drop-offs in the thick tangle of trees and ferns where her college friend Amanda Eller vanished last month.
"You have to search everywhere," said D'Alessandro, who flew in from Maryland. "You have to go down to that stream bed, even though you don't want to. She could be down there."
D'Alessandro and others gathered GPS data of the ground they covered, and organizers put it on a specialized digital map to help better understand where to look next.
The technology led volunteers to Eller, who was found next to a waterfall and survived for 17 days in the Maui forest by eating plants and drinking stream water.
Her dramatic rescue shows how emerging technology helps search teams more efficiently scour the wilderness for missing people.
"It kind of led us to search outside of that high-priority area to where we actually found Amanda," her father, John Eller, said.
More U.S. teams are turning to the technology that combines cellphone GPS with digital maps detailing cliffs, caves, waterways and other hard-to-search terrain. It helps manage the work of large numbers of volunteers.
The system showed when Hawaii searchers had covered a 2-mile (3-kilometer) radius around Eller's car.
After that, searchers sent a helicopter farther into the forest, where they spotted the 35-year-old physical therapist and yoga instructor.
"We never would have pushed out if we hadn't searched the reasonable area first. There's no reason to start reaching further and further out of the box if we hadn't completely searched the box," said Chris Berquist, a volunteer search leader.
David Kovar, advocacy director for the nonprofit National Association for Search and Rescue, said most search and rescue teams use digital maps.
That could mean anything from basic Google Maps to specialized software called SARTopo, which California search and rescue experts used to advise Maui volunteers from afar.
Search organizers in Hawaii asked volunteers to download a $3.99 app called GPS Tracks, which draws lines on a map showing where a user has walked.
Search and rescue teams from Oregon to North Carolina have started using it.
Searchers used it in March as 100 volunteers fanned out in a Northern California forest, eventually finding 8-year-old Leia Carrico and her 5-year-old sister, Caroline, who got lost near their home.
Last month, teams used it to help locate a 67-year-old hiker who had veered off a trail in a state park north of San Francisco.
A California Highway Patrol airplane using an infrared camera spotted the man.
SARTopo also is becoming available as a cellphone app, which will make it even easier to directly connect the GPS data with digital maps so searchers can view them wherever they are.
Government officials are looking at adopting new technology, including in Hawaii.
Most large searches are done by volunteers because many places don't do enough of them to keep official teams on staff.
After technology helped find Eller, her father is donating software and other equipment to Berquist's team, developing a search and rescue app and giving $10,000 to support Hawaii searches and rescues.
"We saw a huge need. And we feel so lucky with everything everybody did for us, so we're looking to give back," John Eller said.