I'll second this but add _without a subscription_. I like the idea of Oura or Whoop but I don't want want the monthly fee, and just want the minimal amount of data (acceleration, heart rate, maybe temperature), in something I can wear along side a legit mechanical watch.

Same. Or a tracker that clips onto any existing watch band. I collect and don't like having the same thing on my wrist all the time.

There is Whoop but the subscription adds up.

Amazon just discontinued that. Halo was a screen free tracker with decent battery life.

I had 2. They were borderline useless at health tracking. HR widely inaccurate. Good for telling you heart is probably still beating but otherwise worse than a just taking a guess/rated perception.

Oura