Knowing that nightfall was quickly fast approaching, the two called 911 for aid because they were lost and were unsure about their positions – eventually, a helicopter was called onto the scene to track down the missing hikers. Unfortunately, they didn't know the exact position of the two hikers, but thanks to some quick thinking by the lost pair, they were eventually rescued.
Specifically, the hikers decided to shine their cell phones toward the approaching helicopter and were quickly spotted because of the night vision goggles that were used by the rescuers for their search. Even with the dense amount of wooded areas, something like the light from a cell phone can instantly stand out while using night vision goggles. Good thing they had their phones on them because they could've been overlooked by the rescuers – thus spending one cold night at the park.
source: UPI via Textually