The Fox 40 Sharx — a pealess whistle with a soft cushioned grip, supplied with a lanyard. Finished in neon / grey.

The cushioned mouth grip is the difference. A hard plastic whistle on cold teeth in February is unpleasant enough that people stop using it; the Sharx has a soft overmould that makes it comfortable to blow repeatedly.

That matters more than it sounds. A whistle you are willing to use three times in a row is better than one you flinch from.

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.

Three blasts, repeated, is the recognised distress signal. One blast means I am here.