AS much as Paul Hardin wants you to buy his products, he hopes you never have to use them. That’s because more than half of the people who do turn on his outdoor rescue devices “are at the point of death,” he said, and are otherwise out of options.

The products, called personal locator beacons, “are really devices of last resort,” said Mr. Hardin, vice president for sales and marketing for A.C.R. Electronics, a leading manufacturer of the beacons, which give lost hikers or stranded climbers a way to alert search-and-rescue teams at the push of a button.

After years of being used by private pilots and boaters, the beacons were approved by the Federal Communications Commission for use on land in 2003. But until recently, they have not sold well. The recent spike in demand followed two fatal headline-making events in Oregon last year: the deaths of three climbers on Mount Hood and the death of James Kim, who left his stranded family in the frigid, rugged mountains of southern Oregon to seek help on foot.

Even with the increased demand, there were only 18,006 of the devices registered in the United States at the end of last year, according to the National Oceanic and Atmospheric Association, which administers the rescue program.

The primary reason is price. A.C.R.’s models cost $550 to $650.

Another reason is weight — they are generally 10 to 14 ounces. That doesn’t sound like much, but backpackers and climbers are always looking for ways to carry less weight. “Weight is a big issue for exactly the kinds of people P.L.B.’s are meant for,” said Doug Ritter, publisher of Equipped to Survive, a Web site that features product reviews and advice on outdoor survival equipment.

Older or less-expensive personal locator beacons use Doppler radar to determine the user’s location. Newer, costlier models include Global Positioning System technology, which pinpoints the user’s location faster and more accurately.

Once the device is triggered, the signal is repeatedly transferred to various agencies until it gets to the team of potential rescuers. The signal is sent from Cospas-Sarsat to N.O.A.A., which alerts the Air Force Rescue Coordination Center, which in turn alerts state and local rescue personnel — a park ranger or sheriff’s office, for example — as well as the user’s emergency contact.

That sounds like a long process, but on average rescues using Doppler radar are started in less than 90 minutes. If the beacon is equipped with G.P.S., it takes just 4 to 17 minutes, according to Mr. Hardin of A.C.R.

It is important for device owners to fill out registration forms as completely as possible, Mr. Hardin said. Glitches can occur. “If G.P.S. doesn’t acquire and Doppler doesn’t work, but you did a good job with the registration, they can still find you.” Adding your itinerary in the comments section is a good idea, he added. “At least then they have a general idea where you are.”

Adventurers in trouble are advised to try a cellphone first. But when a cellphone signal can’t be obtained — a common situation in remote areas — the beacon comes into play. Advocates say the locators are vastly more reliable than satellite phones, which cost far more than the beacon.

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A.C.R., based in Fort Lauderdale, Fla., says it sells more than half of the devices used in the United States. Two other companies make most of the rest: McMurdo, a British company, and Microwave Monolithics, which is owned by the same British company, Cobham, that owns A.C.R.

A.C.R. makes two models. The TerraFix comes with or without an internal G.P.S. unit, but either can be hooked up to a separate G.P.S. device. It is 5.7 inches long, slightly more than 3 inches wide, and 1.74 inches thick. It weighs 12 ounces. Like all personal locator beacons, it runs on factory-installed lithium batteries that must be replaced by a certified dealer within five years. Outdoor supply stores, like R.E.I., L. L. Bean, Backcountry.com and Bass Pro Shops, sell them for about $450. The TerraFix with an internal G.P.S. unit costs about $100 more. A.C.R.’s newest model, the MicroFix, weighs 10 ounces and comes equipped with G.P.S. It is 5.85 inches long, 2.21 inches wide, and 1.4 inches thick. It costs about $650.

Both models have a battery life of more than 24 hours at minus 20 degrees Fahrenheit and both are waterproof and will float if dropped in water.

Continue reading at:  https://www.nytimes.com/2007/07/05/technology/circuits/05basics.html