Signal mirrors have been used by the Worlds Militaries for many years. Some armies used them as recently as in the 1960’s. They were used by the resistance against the Soviet invasion of Afghanistan and probably have been used against us by the Mujahideen. The US military still issues them for rescue purposes in survival kits.
The system used by militaries in the past was a heliograph. This was a mirror in varying sizes that had a cover over the mirror so that it could flash a coded signal. The distance that heliograph signals could be used depended on the clarity of the sky and the size of the mirrors used. A clear line of sight was required, and since the Earth’s surface is curved, the highest convenient points were used. Under ordinary conditions, a flash could be seen 30 miles with the naked eye, and much farther with a telescope. The maximum range was considered to be 10 miles for each inch of mirror diameter. Mirrors ranged from 1.5 inches to 12 inches or more. The record distance was established by a detachment of U.S. signal sergeants from stations on Mount Ellen, Utah, to Mount Uncompahgre, Colorado, a distance of 183 miles on September 17, 1894, with Signal Corps heliographs carrying mirrors only 8 inches square.
Today mirrors are used to located lost individuals. The best mirror is the one issued by the U.S. Military. There are currently many knock offs on the market. Some good, some bad. I have one sold by Adventure Medical that seems to be quite adequate Beware of cheap ones.
These mirrors are easy to use and have a sighting hole in the middle. To use hold the mirror up to your eye and look through the sighting hole. Find the point of reflection or bright spot and aim it at your target. When you first go to use it, you may find it easier to locate the reflection, if you hold your other hand out and let the bright spot hit it. Once you have found the bright spot aim it at your target. This is easier than it sounds, but try it before you need it.
If you don’t have signal mirror with you, there are many ways to improvise one. Everything from a tin can lid with a hole punched in the middle to an old CD or DVD will work. If you don’t have a hole in your signaling device, you can make it work by holding one hand out in front of you with two fingers in a V. Focus the bright spot on the V, an aim at the target by looking through the V.
Signal mirrors can be used for many things, from rescue to transmitting simple codes. This is a very effective low-tech way of communicating in a situation in which you have no electric power or working radios. In an emergency, they can be a very useful tool. But as with any tool, proficiency comes with practice.