Oura. 2 people have talked about it publicly.
Used to check he gets about seven hours of sleep
Sinclair said he wears an Oura Ring to monitor his sleep duration.
“monitor I'm getting seven hours by wearing an Oura Ring”David Sinclair
Source: A Day in the Life of Professor David Sinclair (interview)
Used with Apple Watch to track sleep
He tracks his sleep with an Oura ring and an Apple Watch.
“Also track my sleep with my Oura ring, Apple Watch.”Mark Hyman
Source: My Personal Longevity Routine - Transcript (The Doctor's Farmacy ep. 687) (podcast)
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