When Amanda Eller went missing in Maui in May after leaving for a hike, rescue teams worried they would have difficulty locating her in densely tangled forest filled with steep cliffs. A new GPS tool changed that.

Eller’s friend, Yesenia D’Alessandro, joined a 100-strong search party hoping to find the 35 year old physical therapist who also teaches yoga. Many of the search and rescue volunteers had downloaded a GPS app, called SARTopo, to their phones before departing into the wilderness.

The app gathered data about what areas had been searched so that rescue teams could create maps and narrow down areas still to look through. Available for $3.99, the app tracks where a volunteer walks to create a detailed look at what area has been covered.

The app allowed volunteers to refine their search methods and discover Eller, alive after 17 days of being missing, next to a waterfall. Eller had been surviving off of foraging for wild plants and sipping water from streams to combat dehydration.

The app, which led to Eller’s rescue, will hopefully lead to more successful search and rescue missions in remote wilderness areas.

“It kind of led us to search outside of that high-priority area to where we actually found Amanda,” her father, John Eller, said in an interview with the Associated Press.

In the United States, the app has allowed rescue team organizers to chart and map areas of wilderness to better inform volunteer search parties of the terrain.

The GPS system that helped volunteers find Amanda Eller showed that search parties had covered a two mile radius around Eller’s abandoned car without any luck. Helicopters were then sent in to search a wider area, which is when they found Eller.

“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 speaking with the Associated Press.

The data from the GPS app showed rescue team organizers that volunteers had actually been covering a lot of the same areas repeatedly, with cliffs blocking their routes and forcing them to turn back and dense greenery creating confusion as to which direction to take. This helped the leaders create a better plan to push volunteers into areas that had not been covered yet. Any kind of natural barrier to volunteers, such as water or cliffs, was searched via drone or by rappelling experts and divers.

The tool is growing in popularity across the United States. In March, rescue workers used the app to find two girls in a Northern California forest after they had gotten lost. It was also used to recover a 67 year old hiker who went missing during a hike near San Francisco.

And Amanda Eller’s father, who was so grateful to have his daughter home safely, has decided to donate supplies and $10,000 to help further rescue efforts in Hawaii and improve the app to save time during rescue missions.

“We saw a huge need. And we feel so lucky with everything everybody did for us, so we’re looking to give back,” said John Eller.