I use a Huawei wrist band I got for 30 EUR. It tracks your REM/deep and light sleep. I would say accuracy is good but not exceptional. All fitness bands brands

I use a Huawei wrist band I got for 30 EUR. It tracks your REM/deep and light sleep. I would say accuracy is good but not exceptional. All fitness bands brands (Huawei, xiaomi, Fitbit) today track your sleep. You can give it a try and decide by yourself.