Quillfred, I should have checked out the air horn you talked about before I wrote my message. I see that it's not what I have but a whole lot more effective. This is what I read:

A bike horn that won't be ignored. The Air Zound 2 from Delta is a handlebar mount rechargeable bike horn that will satisfy that urge to be loud and annoying. It offers 115 dB at the touch of a button with volume control. The air reservoir is rechargeable with any bicycle pump.

Sounds very interesting. Thanks for the info!