Doesn’t work as it notifies the person traveling with it.

Of you hide it well enough? I can think of some creative spots in a car, like behind the dash, in the door, inside of the a seat, etc.

If the thief has an iPhone, they will see this: https://sm.mashable.com/mashable_pk/image/default/uploads252...

It's quite easy to clobber the speaker

It still alerts (UI Prompt) on any iPhone that it travels with for too long (~24hr).

I thought it only chirped if the owner clicked that option in "Find My" app.

Its not that it is chirps it is that any iPhone beeing tracked by a airtag for a extended amount of time will inform its owner that it is being tracked.