To convey the message under water we need to use diving signs. But to be able to show them to other devices we first have to somehow get their attention. How to do it? Using sound signalling devices. Here they are.
Nothing could be simpler. Just string a bead on gum and attach it to the bottle. When we want to use this invention it is sufficient to pull the bead from the bottle and let it go. The best solution is to repeat the operation several times.
A magnetic shaker
An important advantage of the shaker is that there are no failures of it. It has a very simple structure – a magnet and a ball inside a tube. Moreover it makes sound only when it is needed – simply shake it vigorously. It does not make sounds during diving. It is very light. It works when the rest of the divers are located within a short distance.
A pneumatic hammer
This device works thanks to compressed air that is why it connects the inflator and the inflator hose. The button on the hammer causes that the hammer makes very clear sounds of knocking with a range even up to 200 meters. The disadvantage of this solution is that it uses air. It is also the most expensive from signalling devices.