You're concerned about it being too loud for things that can hear it. Well, at 5V/35mA, the sensor that you mentioned consumes an average of 175mW while operating. Not all of that gets converted to sound, of course, but we can get a rough idea of what we're working with by assuming that it does.
According to this site, 1W of purely acoustic power is 112dB at one meter away from a point source. That is, 1W spread over the surface of a 1m radius sphere would measure 112dB at that surface. Considering that we only have 175mW instead of 1W, that's \$112dB+10dB*log(0.175) = 104.5dB\$, still on the surface of a 1m sphere.
Now we have two conflicting modifiers:
- There are other functions besides the transducer, which itself is less than 100% efficient, so we actually have less than 175mW of acoustic energy to convert to dB.
- It's actually a spherical section (cone with a round base), not a complete sphere, so the same power is spread over a smaller area and is therefore more intense at the same distance. (in RF, this is called "antenna gain")
The relative strength of those modifiers is up to you to figure out, with a few guidelines:
- "One-note" or resonant design goes a long way towards ideal efficiency.
- A large transducer compared to the wavelength being produced increases both efficiency and directionality.
- This is why subwoofers need ridiculous amounts of power and can be heard everywhere while tweeters are pretty much the opposite. What you've got is practically a "supertweeter".
- For a point source (expanding sphere or spherical section), you lose 6dB for each doubling of distance, simply because the area that it's spread over increases at that rate.
- For completeness, a line source (expanding cylinder or cylindrical section like a highway or line-array speaker set) loses 3dB because the area increases more slowly, and a plane source (large surface like a wall, ceiling, or floor) doesn't lose any because the area stays constant. But at some distance relative to size, all finite-sized sources in open space eventually reduce to point sources and so they all ultimately revert to the 6dB rule.