Survival Kit: Signal Mirror
February 24, 2012, Submitted by: Ken Tweet
A signal mirror is one of the many things that you could choose to add to your survival kit. It is a tool that could save your life. A signal mirror is, you guessed it, a mirror – but it’s design and purpose is to alert others of your location.
An ordinary reflective mirror is better than nothing, and will work if handled properly. The thing is, 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 something called retro-reflecting material, or a retro-reflective mesh style ‘aimer’.
“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 cannot be beat. Here’s one that I found online:
You know what is so nice about these is that they are the size of a credit card and can be kept in your wallet just in case. Here’s something really positive, instead of that extra credit card in your wallet ready to poison you with more debt, keep one of these signal mirrors in there instead.
This mirror is glass. I’d test it for durability before I put it in something that I sit on.
Even if it breaks it is better than a credit card. The credit card will break you. lol
Be well.
Although it is a glass mirror design, a glass mirror will produce a significantly better reflective flash than plastic imitations. The drawback though is you need to be fairly careful not to break it. On the other hand, other non-glass models will scratch very easily and reduce effectiveness. There are always trade-offs it seems.
True.
I was suggesting that you might not want it in your wallet.
Be well.
Here’s a polycarbonate version for under $13.
[edit-insert-link] Starflash Signal Mirror
Nice article! Love the graphics!
The US Coast Guard conducted testing in 1944 that concluded that retroreflective aimers were vastly superior to other aiming methods (even before the author developed the mesh aimer). British testing came to the same conclusion. The article below describes the US testing, and is also a good history of the WWII development of US military signal mirrors.
“Heliographic Signaling Mirrors”, by Richard S. Hunter
Pages 24-29, 48 Air sea rescue bulletin. v.3 no. 3 1946 Washington, D.C.
http://babel.hathitrust.org/cgi/pt?id=mdp.39015010566720;seq=86;view=image
(The test results are summarized here:
http://babel.hathitrust.org/cgi/pt?id=mdp.39015010566720;view=image;page=root;size=100;seq=110)
When buying glass signal mirrors, the consumer does have to be wary that the mirror has real retroreflective material in the aimer, and not a non-functional “lookalike” that does not produce a usable fireball. There’s a cautionary article about the lookalikes (with lots of other good info) here: http://www.equipped.com/phony_signal_mirrors.htm
The link you provide above is to a genuine US military signal mirror, and the similar commercial glass signal mirrors sold by Coghlan’s and Vector I are fine, too.
You can, indeed, see the flashes from the 2″x3″ glass mirror at 22 miles in good visibility (though closer or larger is much more visible) – I tried this with a friend and posted the results on YouTube here:
http://www.youtube.com/watch?v=sxOvip1gtB4
A hiker was rescued in Santa Barbara earlier this year thanks to their signal mirror: http://www.edhat.com/site/tidbit.cfm?nid=78545
and I maintain a log of recent (2005+) signal mirror rescue news stories here:
http://forums.equipped.org/ubbthreads.php?ubb=showflat&Number=199083#Post199083
You mention the “D” version of the MilSpec – the “E” version can be downloaded freely here:
http://www.assistdocs.com/search/document_details.cfm?ident_number=12866
If you have a nice .pdf scan of the “D” version of the MilSpec, I have other scanned signal mirror docs I could trade for it (such as a version of the Hunter article where the edges aren’t trimmed off) – drop me a line at my email address.
Richard, Thanks for the Very Informative reply and interesting links. Good stuff! The video is amazing, to see the signal mirror in action at 22 miles! Wow. The power of the sun…
A CD can be used quite effectively for emergency signalling; it is reflective and has a hole for sighting. It doesn’t hurt to keep a couple of bad ones around for that purpose, especially in the car.