Galaxy Watch 3 have the ability to track your sleep when you wear your watch to bed. It can track the different sleep stages, including REM sleep, and provide insight in your sleep quality on a nightly basis.
Please refer to the link to check all the information and specifications. https://www.samsung.com/ae/watches/galaxy-watch/galaxy-watch3-45mm-mystic-black-sm-r840ntkamea/
Hope that helps!