My Airzound just failed, after the 2-3 years mentioned by others. In my case, pressing the button failed to produce any sound, although there was some air left. In the interest of science, I took it to pieces to find the reason for the failure, and discovered that the valve had rotated whilst I was screwing on the pump and twisted up the air line, blocking the flow. This is not normally a problem, as I usually use a track pump which is a push fit, but I occasionally use an screw-fit pump when I am riding.

There does not seem to be a cure for this once it has happened. The air line is a push fit onto the valve, but there is no way to connect up a new air line, and it looks like the valve and airline are put in place before the final assembly of the horn.

I have a new horn coming, and the first thing I will do it apply Sugru to the base of the valve to stop it rotating. I could not tell whether the valve was originally glued or whether it was just a friction fit keeping it in place, but the twisting of the airline seems to explain a few of the failures here. It is also possible that the airline gets weaker and more prone to twisting with age, particularly around the valve.