Signal whistle and signal mirror: basics

A whistle tone is high and shrill. Tones like this stand out well from wind, rustling leaves and many other natural sounds, and the ear picks them up easily. In addition, blowing a whistle only needs a short, strong breath. Shouting is tiring, and after a while your voice gives out. With a whistle you can attract attention for much longer.

A mirror does not collect light, it redirects it. The sunlight that falls on the mirror is thrown in one direction as a concentrated spot. Anyone standing or flying exactly in that direction sees a bright flash that stands out clearly from the landscape. The skill lies in steering this light spot deliberately onto the target – because nobody beside the target will see it.

A proven method goes like this: stretch out one arm and make a V with two fingers so that you see the target in it – for example an aircraft or a hut. Hold the mirror close to your face with the other hand. Tilt it slowly until the bright light spot falls on your fingers. Then let it sweep a little further across the target and back again.

Many signal mirrors have a small sighting hole in the middle that makes aiming easier. In any case it helps to practise aiming beforehand, for example at a light-coloured wall or a tree trunk some distance away. Aiming a mirror for the first time under stress in a real emergency is hard.

If you cannot see a target, you can slowly sweep the light spot across the horizon or along distant paths and slopes. Someone may be there whom you cannot see, but who can see you.

Give short, strong blasts in a recognisable rhythm. In the Alps the alpine distress signal is customary: six signals per minute, then a minute's pause. Elsewhere three blasts are often understood as a call for help. In any case it is important to be quiet between groups of blasts and listen for a reply.

A good signal whistle has no ball inside that could freeze or stick in the cold, and it works even when wet. Attach it so you can reach it with one hand and while wearing gloves – for example on a short cord on your shoulder strap. Children should carry their own whistle and know when they may use it.

Flashes of light can dazzle. Never aim the mirror at drivers, cyclists or people near you. Once an aircraft or helicopter has clearly noticed you – for instance because it turns towards you or circles overhead – stop flashing into the cockpit and show yourself with body signals instead. A glass mirror can break; then there is a risk of cuts.

Do not blow the whistle right next to other people's ears – a shrill blast at close range can hurt. Above all: whistle and mirror complement an emergency call; they do not replace it. As soon as you have signal, dial the local emergency number (112 in the EU). Never give distress signals for fun, because others might alert rescuers.

Whistle and mirror are light, cheap and need no batteries. That makes them a good backup for a phone and a beacon. Signal mirrors are made of glass or of break-resistant plastic; plastic is lighter and does not shatter, but often reflects somewhat less strongly.

If you have no mirror, other shiny surfaces can help: the silver side of an emergency blanket, a phone screen, a CD or a polished piece of metal. They usually reflect more weakly and are harder to aim, but it is worth a try. At night a headlamp or torch takes over the mirror's role – in the same rhythm as the whistle blasts.