The OEM Ulefone has launched its new Watch series, which support continuous heart-rate tracking, multiple sports modes and 5ATM water-resistance. There is also a blood-oxygen sensor in the Pro model, whereas the Watch GPS has additional activity-tracking features. They start at US$49.99, or even less with a limited-time introductory offer.
https://www.notebookcheck.net/Ulefone-announces-3-new-fitness-focused-smartwatches-at-sub-US-70-prices.501403.0.html