Last July, two hikers were on a backpacking trip in California’s Shasta-Trinity National Forest. Just northeast of Granite Lake—a small body of water edged by deadfall and a rocky mountainside—one of them fell and was too badly hurt to continue.
From their supplies, they pulled out a personal locator beacon. They extended the device’s antenna and pressed the button beneath. Immediately, a radio signal began beaming out at 406 megahertz, eventually hitting detectors on orbiting satellites. These instruments, part of the National Oceanic and Atmospheric Administration’s Search and Rescue Satellite-Aided Tracking program (Sarsat), picked up the signal and immediately pinged alerts to Earth.
Someone’s in trouble near Covington Mill, California, the
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