Smartwatch sleep recording?

I have a smartwatch from huawei. One of the features is sleep recording. Does anyone know how reliable such a sleep recording is? I read on the Internet that sleep is measured based on the pulse rate and movements. Somehow I don't really believe it. It is clear that this measurement is not as accurate as a sleep laboratory.

You already gave yourself the answer… It is not as precise as in the sleep laboratory.

There's actually nothing more to say.

If you want to have a reasonable sleep test, then only a sleep laboratory is an option. Everything else is gimmick.