Fitbit, now owned by Google, is currently evaluating if it can add blood pressure monitoring as a new feature for the Fitbit Sense, among others. Apparently, Pulse Arrival Time (PAT) may make it possible for Fitbit to do so. Fitbit will be testing blood pressure monitoring on the Fitbit Sense for the next month and will let people know if they can participate in the study.
https://www.notebookcheck.net/The-Fitbit-Sense-may-be-able-monitor-blood-pressure-soon.531562.0.html