I have few suggestions to anyone that wants to develop refferee signaling system for uwh.

Such a system does not need to work underwater at all! What it needs, is to have a watertight casing and antennae mounted on the refferee's cap or top of the snorkel. It can be even easier to use already existing system and adapt it to become watertight. This should be simple and cheap solution. It needs to work only at 3 different frequencies, as there cant be more than 3 playing grounds in the same arena. Dont forget to put a button on the buzzer, as when it won't work, refferee's will have an option to do it the old way. For all it goes, if you can find a hand-held electronic remote trigger for any aplication, you can use the same electronics, and mount it in a watertight casing, and there you have it. Instant buzz, but only when ref puts a hand out of the water.
Chief ref will have easier job, watching the fauls on the surface and substitution.

There is even another way to do it, but the buzzer will have to be small enough and have small energy usage. Mount the buzzer on the refferee ( very small backpack), and there is no need to transmit any signal. One small watertight box will be all thats needed. The buzzers will have to have 3 different sounds. This might be even easier to make, cheaper and more reliable system. Instant buzz period.

And there is even a third system, thats the easiest to do. Put small scuba tank (1 liter up to 5) in the small backpack (or mount it on a backplate, preferrably plastic not stainless). On the tank, mount some old 1.st stage on it, with only one low pressure hose, and mount a scuba buzzer on the end of it. 1 liter tank shoud be enough for several games, 5 liter for all of the tournament. A regular scuba tank of 15 or 18 liter, and a high pressure hose can easilly re-fill the smaller tank when its needed, in much less then 3 minutes, witch is the usual time between the local games. For bigger championship, there is a need to find 2 or 3 distinct sounds of the buzzer. For those that never scuba dived, scuba buzzers are very loud, and just about every scuba shop sells them, and can make this system for you, just by reading my post. Total cost should be under 100 eur per unit. There is NO servising cost, and such a system is bound to work for long long years, just remember to make A-testing of the small tank every 2 years (you dont want to have a tank explosion). Instant buzz anywhere, for cheap money.

Rudi