Wow, I rented a MB once and it did that, which was absolutely the right call. The thing was that I initially ignored it and thought MB used a timer or something but 15 minutes later, I became aware of it and it was quite acute by the time I was aware of it.

I've always wondered how it knew that.

Do you have a source for this? My understanding is the Mercedes "Attention Assist" is based off driving behavior and not a camera pointed at the driver.

mb doesnt use a camera.. it's based on your steering wheel inputs.

There is at least one manufacturer doing it though: DS has "driver attention monitoring" which does use a driver facing camera.

wikipedia has a good list of what manufacturers are using: https://en.wikipedia.org/wiki/Driver_drowsiness_detection