Usually they're tolerable, just annoying.
The screenshot is from one I found installed outside Lidl (supermarket) now, above the entrance. Probably loud enough to "cover" the entire parking lot. Loud enough to get painful after a few seconds. Sweeping between 15.5kHz to 18.7kHz. For comparison, a CRT TV is around 15.7kHz.
I wonder if not caring about loudness of these higher frequencies contributes to hearing damage among people.
Lower frequency, but also awfully loud buzzers can be found in trains near doors, working as a warning when the doors are closing. Thankfully, this probably annoyed some of the staff enough for them to start taping these over.
But those are loud enough to sound distorted.
Anyway, I just hid behind a corner where I couldn't hear it that much while waiting for the manager to call us in.
Possibly adults too. I tried to find limits, but there's many different standards. Most seem around 70 - 75 db for up to 20kHz, then wary between 85 - 110db above that, which is... quite the range.
But also, these are probably rather meant for work environments, so possibly 8h/day with ear protection. Only ICNIRP mentions limits for public, being 70db up to 20kHz and 100db up to 100kHz.
The lowest I found is quoted from USAF in this review of standards of 85db up to 40kHz.
Now, for example this piece of shit boasts 130db in 20 - 27 kHz range: https://www.leaven.com/en/product-213036/ULTRASONIC-PESTREPELLER-LS-968.html