Replying to my own comment, but it looks like there's at least one device on the market that measures BP without the wearer knowing it's being done, the Aktiia Optical Blood Pressure Monitor.
Cost about $250-300. It's not available in the US right now officially, though it's cleared in several European countries. I don't know if it's legal to import. If it is, I may well do so.
Cost about $250-300. It's not available in the US right now officially, though it's cleared in several European countries. I don't know if it's legal to import. If it is, I may well do so.
Regrettably it has a cloud connection.