I dove recently with someone that has a noise maker that is the most effective I have heard. Effective in that it is very audible and not obnoxious. It is about 2 inches long, looks like a dive tank and sounds like ringing bells when it is shaken. It has an SAS stamp on it. He told me a friend from Japan gave it to him. I've done a fair amount of searching on the web, but I can't find it and I'd really like to have one. Is anyone familiar with this product?