Yes Fred, it works on commpressed air. Its a divers way of reffereeing .

I cant upload pictures today, becouse I lend my cables. But I'll upload eventually. Anyway, I'll bring the units on championship. One unit will have 4 liter tank, and one will be 1 liter. I'll try to make the neoprene shield until then.

But the whole sistem should include buzzer for the chief refferee also. The tank for the chief refferee should be 15 lit, and used also to refill the small tanks. The thing is, that in order to work properly, I need more time. 2 days isn't enough. It needs about 2 meter LP hose for the buzzer to be in the water, and I'll have to "adapt" industrial pressure switch between the hose and 1.st stage. This way, It will be easy for the chief refferee to push on the switch, becouse the switch will be on the tank, and not on the buzzer. I hope you understand what I'm saying. I can put 2 hoses on the tank, so there will be two buzzers, one for underwater, and one for outside water (these buzzers are not the same). Both will be engaged by the same switch.
I'll do that only, if most of refferee's like the sistem and wants to use it. These 2 units costs me nothing, I borrowed all of the elements from 5 different friends

Fred, you'll be the first to see the units, just find slovenian team on friday. Probably I'll be in some pub.... :-)