A signal mirror is a mirror – but with a way to exactly aim it where you want, so as to alert others of your location by its flashing reflection of the sun.
While an ordinary reflective mirror in your survival kit is better than nothing, it will not be as effective as a mirror designed to be a ‘signal mirror’ which includes features that help you to aim the mirror precisely at the target (an aircraft, ship, vehicle, spotter, etc.).
The secret to a true signal mirror is this…
…”retro-reflecting” material, a retro-reflective mesh which assists while aiming the mirror.
“Retro-reflective” means that the light is reflected back to the source. In the context of a signal mirror aiming device (the round hole and mesh in the middle), this material consists of tiny glass beads glued to a mesh screen, which creates a fireball on the mesh (an image of the sun), which is used to indicate where to point the mirror. You tilt the mirror to overlay the fireball on your target.
The original patent for the signal mirror (# 2,557,108) was issued in 1951 to inventor, Richard Hunter.
A few key notes from the Mil-Spec…
Military Specification MIL-M-18371D(ASG), Mirrors, Emergency Signaling
- 2 different types of signal mirror, a 2×3″ and a 3×5″
- 2 layers of glass laminated together with a sighting device and lanyard
- Wide angle retro reflecting material for sighting
Signal Mirror Aiming Instructions
- Reflect sunlight from mirror onto a nearby surface, hand, etc.
- Slowly bring mirror up to eye level and look through sighting hole. You will see a bright light spot. This is the aim indicator.
- Hold the mirror close to the eye and slowly turn and manipulate it so that the bright light spot is on the target.
- Even though no aircraft or ships are in sight, continue sweeping the horizon, for mirror flashes may be seen for many miles, even in hazy weather.
Note: Never look directly at the sun, that includes through the aiming hole!
Not every signal mirror is made from glass. In fact most are made with plastics and other reflective coated materials for lighter weight and cost. However, the signal flash produced from a glass mirror is far brighter and more effective.
Here is a signal mirror made by S.I. Howard in the USA, a military approved and issued item. It’s what I keep in my kit:
Once you get used to how it works, it becomes very obvious as to the advantage and usefulness of the reflective mesh material and the ‘fireball’ that is created on the mesh when you are aiming the mirror properly at the target.
While out walking the dog today, I took a few pictures which hopefully shows the effects. (The pictures and exposure doesn’t do it justice though… the mesh fireball is much more evident in real life)