> Does that not trigger an audible alarm by default in a Tesla

No. That's a standard warning that triggers every few minutes if the car can't sense your hands on the wheel. If you don't place your hands on the wheel at that point, then there will be an audible alarm. If you ignore that, the car will slowly reduce speed and come to a halt.

It's definitely every few minutes. I can attest to that from personal experience. Alternatively, you can just keep your hands on the wheel and then the warning doesn't come up.

Not unless you ignore it, then it will beep, then flash red. I think it doesn’t make an audible sound initially so it proves you are paying attention the whole time rather than only when it beeps at you.