I found a smart ring that rivals the Oura 4 but costs less (and has no subscriptions)
Briefly

The article critiques the battery lives of most smart rings, noting they often disappointingly last only five to six days instead of the advertised week. However, the RingConn 2 stands out with a marathon battery life of 10 to 12 days and a reasonable price of $300, avoiding subscription fees for health data access. Its design is comfortable, with various size options. Additionally, it comes with a charging case that keeps the ring powered for over 150 days, addressing issues faced by users juggling multiple devices.
Many smart rings claim to last a week's worth of battery life, but often they fall short, usually lasting just five to six days before needing a recharge.
The RingConn 2 sets itself apart by offering an impressive battery life of 10 to 12 days, without requiring a subscription for full access to health data.
Unlike other high-priced smart rings, the RingConn 2 is reasonably priced at $300 and offers a comfortable fit, making it a solid choice for wearable tech.
The smart ring's case can power the device’s battery for over 150 days, allowing for convenient charging without constant outlet access.
Read at ZDNET
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