According to new rumours, the Pixel Watch relies on the same health tracking sensors that Fitbit includes in the Charge 5 and the Luxe. The Pixel Watch could debut in May alongside vanilla Wear OS 3 at Google I/O 2022 alongside the Pixel 6a.
https://www.notebookcheck.net/Pixel-Watch-rumoured-to-launch-with-the-same-sensors-as-the-Fitbit-Charge-5-and-Fitbit-Luxe.615632.0.html