Actually, I can hear it, but only just, at the very edge of my hearing.
Even though I can hear the sound when I’m listening for it, though, I’m not sure I could make it out in a crowded classroom.
In the usual double standard way, while I’ve heard some indignation from adults about the teen call phone use of the sound, I haven’t heard any indignation about the shopkeepers’ use. Even though, you know, playing a high pitched tone to irritate young people into leaving your store isn’t any more polite than taking calls in class.
ETA: here’s the sound with crowd noise in the background. Much harder to make out this way.
Also ETA: A web search does reveal some irritation at the shopkeepers after all–and more amusement at teens turning things around, too–than I’d first assumed.