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.”
They also offer thorough instructions on choosing and using a proper signal mirror.
There is much at Equipped to Survive that is worthy reading. Their analysis of signal mirrors suggests that the Star Flash Signal Mirror (available at Amazon) made by Ultimate Survival is among the best.