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.