Everybody knows a signal mirror can save your bacon if you’re lost in the wilderness, but how many of us actually know how to use one? At risk of posting something of actual use to actual hikers, here’s a link with an illustration showing exactly how to use a signal mirror (you have to scroll down a ways for all the details– it’s on a page for small-aircraft pilots).
The item also weighs whether people should bother with old CDs like the ones AOL used to mail out in quantity. The conclusion: No.
In tests a CD proved to be only about 20%-25% as effective (distance and brightness at distance, judged subjectively) as a 3 x 5 mil-spec plastic signal mirror, a bit more effective, but not even 50% compared to a small 2 x 3 mil-spec plastic signal mirror. It would compare worse against higher quality mirrors.
From an operational persepctive, in an After-Action Report of a major SAREX (Search and Rescue Training Exercise) conducted in 2001 by the Colorado Wing of the Civil Air Patrol, the conclusions were, “that “victims” who had never used a signal mirror (with the aiming hole in the middle) were able to use them effectively, while CD’s (AOL etc.) are useless as signal mirrors.”
A good signal mirror can send a flash for miles, but it has to be aimed at at somebody who’ll see the flash.