The Fox 40 Classic — the original pealess whistle, and the one on most referee lanyards in the world.

Pealess means there is no cork ball inside. The old pea whistles jam when they freeze, choke when they get wet, and the pea eventually rots or sticks. A pealess whistle has no moving parts at all, so it sounds the same soaked, frozen or packed with sand.

That is why it ended up in safety kits rather than just on sports fields. A whistle that fails when wet is not a safety whistle, and in the outdoors wet is the normal condition.

It is also effortless to blow. You do not need breath you may not have — a short sharp puff is enough to produce the full sound.

Three blasts, repeated, is the recognised distress signal. One blast means I am here. Red shows up well against snow and against dirt, which covers most of where it gets dropped.

Seven fifty. There is no reason for anyone in your group not to have one.