If your goal is just collect sleep data, I personally use my Withings Scanwatch with a leather bracelet, But if you're not willing to keep a watch while you're

If your goal is just collect sleep data, I personally use my Withings Scanwatch with a leather bracelet, But if you're not willing to keep a watch while you're sleeping they have "Sleep analyzer" that you put under your bed to collect Sleeping data, but I never tried it ! The link : https://www.withings.com/eu/en/sleep-analyzer https://www.withings.com/eu/en/sleep-analyzer