How to Use a Signal Mirror

In the early 1800s, a German mathematician, Carl Friedrich Gauss, demonstrated that even a tiny mirror with a surface area of 1 square inch (6.5 square centimeters) could reflect flashes of sunlight that could be seen over a distance of 7 miles (11 kilometers) [source: Coe].

In the 1860s, a British Army officer named Henry Christopher Mance, who was stationed in India, got the idea of using Gauss' discovery to send coded messages. He developed the heliograph, a special tripod-mounted mirror with a lever that tilted it, so that it could transmit flashes of light of different lengths.

That enabled a mirror to be used to send Morse code, the same system of dots and dashes developed to transmit messages over telegraph wires. While a flash of light from a mirror couldn't be transmitted as far as a telegraph message, Mance found this an ideal way to communicate in the rough, mountainous areas of northern India and Afghanistan. By the late 1800s, the U.S. Army was using relay networks of heliograph stations to send messages through the vast desert expanses of Arizona and New Mexico [source: Coe].

By the early 1900s, radio had taken the place of the heliograph for most routine military communication [source: Coe]. But mirror communication didn't go away. During World War II, U.S. Navy pilots carried mirrors in their survival kits, so that if they crashed or were shot down, they could get the attention of rescuers [source: Flying Magazine]. In 1960, a Life magazine article by Mercury astronaut Alan Shepard noted that in addition to a battery-operated radio transmitter, he carried a signal mirror to help recovery ships locate him in the ocean [source: Shepard]. Today, signal mirrors are still recommended to military personnel and adventurers alike as a device to always have on hand.

In the next section, we'll tell you how to find a good signal mirror.

In a pinch, you can use almost any reflective surface — even the shiny material from the inside of a broken cell phone — as a signal mirror [source: Galloway]. But survival experts say that you'll have the best chance of contacting rescuers if you use a mirror specially designed for signaling. You want one that's big enough to comfortably fit in your hands — a 2-by-3-inch (5.1-by-7.6-centimeter) size is good — with a small hole in the middle that enables you to see where you're focusing your signal [sources: McDougall, Nester]. That way, you'll capture the eye of a search team, rather than, say, a deer or squirrel.

Some experts advise buying a plastic mirror that's light enough to be manipulated with one hand and resistant to breaking [source: glass mirrors, which can reflect sunlight much farther. So use your own judgment on that. If you opt for glass, carry your mirror in a Bubble-Wrap sleeve to prevent it from being damaged [source: Nester].

You can purchase a good signal mirror for less than the cost of a pair of pants. One outdoor outfitter's Web site, for example, offers a spiffy model that's equipped with a special viewing window that superimposes a red dot on your target, so that you can pinpoint exactly where you are focusing your signal. It even comes with an attached whistle to help rescuers zero in upon you, and it costs just $15.

Practice using your mirror before setting out on your next outdoor adventure. We have instructions on the next page.

If you're stranded out in the woods or at sea, a signal mirror can save your life — that is, if you use it effectively. Some signal mirrors have instructions printed on one side to help users out. But if you don't have such an aid, here are some basic tips.

You can use a signal mirror in two basic ways. If you don't see anyone in the distance, simply sweep the horizon with the mirror, in hopes that you'll catch the eye of a rescue craft or team that isn't yet in your visual range [source: U.S. Air Force]. But once you do spot rescuers you should aim the reflected light at them, and then send a signal so that they can tell that you're a person out there who needs help.

The technique for using the signal mirror is pretty straightforward.

If you're improvising your mirror, hold up two fingers in a V shape and angle the mirror (or credit card or compact) so that most of the light passes through the V. This will help you to find the bead of light.

It's possible to send detailed messages with a mirror by using Morse code, and some people carry cheat sheets to show them how. But you don't need to do that to be rescued. Just flash the mirror toward your target, and then cover it or turn it away from the target. Do that three times in quick succession. That's the international distress signal, which any rescuer should recognize [source: Nester].

Another important tip: It's crucial to know when to stop signaling. Once a vehicle or aircraft has spotted you and is zooming in to pick you up, avoid flashing reflected light into the rescuers' eyes, so that you don't cause them to become momentarily blinded and crash [source: Murray].