Sound Signalling Equipment
On the surface the cheapest sound signalling equipment, but also the one that presents weaker results, is the vulgar whistle.
SOUND SYSTEMS MOUNTED ON FILLING HOSE
The remaining equipment is usually mounted on the diving vest filling hose, and works with air coming from the 1st floor of the regulator. These devices have a very strong sound and with great range. While some only work on the surface, others also work underwater.
The sound call underwater is basically made by percussion. The simplest way is to hit the knife handle on the bottle. However, the market is full of systems, more or less imaginative, of producing underwater calling sounds. The maraca, for example, consists of an aluminum cylinder filled with steel spheres. When shaking the maraca, the sound produced by the spheres is strong enough to be heard by other divers up to approximately 10m away.
Another very simple device is a rigid plastic piece attached to an elastic band placed around the bottle. To draw attention, the diver pulls the piece by stretching the elastic band and drops it against the bottle. The ball’s knock on the bottle produces a strong sound, like a hammering, audible by divers at a reasonable distance.
This system, such as hitting the knife into the bottle, is only effective if the bottle is not protected by a net or other type of cover.
Maintenance of this equipment should be rinsed with fresh water, dry and store in a protected place.
BEEPS IN WATER MUST NOT BE USED LIGHTLY.