How does Watch Lite SE measure my sleep mode?

Based on your heart rate, blood pressure and motion, Watch Lite SE will determine your sleep mode, specifying the percentage of deep and light sleep.

Watch Lite SE can also monitor your REM Sleep time when the 24h monitoring feature is on.

Please note: The REM Sleep service is only available if you have an active monthly subscription.
Can I use my Watch Lite SE in extreme temperatures?