Having emerged from the depths of Andrea Campedelli's digital archive, it is impossible to understand its function, even by observing it very carefully. Then, reading the description of the Polish company Matter that produced it around 1955, the mystery is discovered.
Designed specifically for firefighters when operating in dark or very turbid waters that prevented the pressure gauge from being read, the device was used to warn the diver that he was running out of air. In fact, when the pressure dropped below the preset value, the balloon began to inflate, leading to an increasingly positive hydrostatic balance that was impossible to ignore. Furthermore, its bulk close to the body was noticeable. The balloon was applied to the first stage in place of the standard whistle, which had the same function but was obviously only effective when the operator was working on the surface.
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