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Yep, that's all they are. To work you need a diaphragm that vibrates and makes a sound, or several sounds, which is blown by air pressure (which you also need) into your TRUMPET STYLE AIR HORNS. They will work on all sorts of conveyances or fixed locations, not just cars. https://www.google.com/search?q=antique+trumpet+air+horns&tbm=i...
Thank you for your input. Your wealth of knowledge is impressive !