A survival signal mirror with a centre aiming hole for sighting on a target.

A signal mirror is the longest-reaching thing you can put in a pocket. Reflected sunlight has been seen from aircraft many miles away — far beyond any whistle, light or fire you could manage on foot.

The aiming hole is what makes it work. Hold the mirror near your face, sight the aircraft or the search party through the hole, and bring the bright spot of light onto the target while keeping it in the hole. Sweep the horizon slowly if you do not have a target yet; aircraft spot the flash before you spot them.

It needs sun, so it is a daytime tool — carry a light or a strobe for the other half. No batteries, nothing to fail, flat enough to live in a map pocket forever.

Practise once in the yard. Aiming a mirror is simple but not obvious the first time, and the first time should not be the real time.