Ultrasonic Air Horn

The air horn is a simple device, essentially some canned-air with a plastic horn on top. When pressed, the air rushes out through an orifice of a size tuned to make a loud noise. The noise an air horn makes isn't a specific note, rather just something right in the middle of the human hearing range where our ears are most sensitive. This doesn't have to be the case.

It's perfectly feasible to make a tone outside the normal human hearing range. You could go low, to make an infra sound, deeper than a fog horn, but this would require a LOT of air and a massive horn. This isn't practical. Making a high frequency is much easier, you need smaller components, and possibly higher pressure which is fine. So what tones are we aiming for... I suggest two separate air horns with different tones.

The first is at around 18kHz. This is above the hearing range of normal adult humans, but, crucially, within the hearing range of teenagers and younger children. It is, essentially a cheap, disposable use-anywhere mosquito <link>. This may be used by a responsible adult in a variety of scenarios where children might need to be distressed without inconveniencing everyone else.

The second model is even higher pitched. say, 35kHz designed to scare off the majority of animals, racoon rooting through your garden... give it a blast of the animal-specific air horn.