Signalling mirror

Fig. 1: Four methods of directing the flashes from daylight signalling mirrors, 1944

Signalling mirrors are handheld devices designed to signal distress by reflected sunlight. Unlike ordinary mirrors, signalling mirrors have integrated aiming aids that let the user accurately direct the reflected beam of sunlight.

Signalling mirrors with effective aiming means are required equipment on the lifeboats and liferafts of oceangoing ships, standard equipment in military survival kits, and carried by hikers and boaters.

Signalling mirrors have a sighting hole and an aiming aid. The aid is a foresight paddle, rear mirrored face, or retroreflective material around the sighting hole. British and American tests found retroreflective aids far superior to the others when signalling from rocking boats.

While ordinary mirrors have been used to signal for centuries, signalling mirrors were developed in World War 2.

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