Another good reason to EDC a decent flashlight. Any light may help - I had to dig for this one, which I remembered reading when it occurred in 2008.

"And a 17-year-old girl who was lost in a remote area of New Zealand, at night, in August of 2008 was found when the crew of a rescue helicopter used night-vision goggles to spot the backlight on the girl's cell phone."

Yahoo News Item - Cellphone Light Guides Rescue Helicopter

I couldn't track down the original article but I believe it was verified.
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Men have become the tools of their tools.
Henry David Thoreau