The story hyperlinked below, datelined 10/29/2010, describes a rattlesnake bite victim in Oregon 2.5 hours from the nearest highway. He contacted his wife by radio, she used OnStar to dispatch a medevac helicopter to their GPS coordinates, but despite the GPS coordinates, the helicopter couldn't locate them on the first two passes.

The OnStar operator asked him if they had anything reflective.
They dug into their hunting kit and found a signaling mirror, which they used to signal the helicopter.

24 vials of antivenin later, all was well.

Good teamwork of modern technology and old-fashioned survival gear!

Link to Full Story of Snakebite victim and Signal Mirror
A signal mirror should backup a radio distress signal, like a 406 MHz PLB (ACR PLB) (Ocean Signal PLB)