Can you show an example of a blood pressure monitor that you are talking about ? I am not a doctor, but I've seen my grandma use a very portable one for a decade now.
Edit: updated IANAD to I am not a doctor
Edit: updated IANAD to I am not a doctor
https://www.amazon.co.uk/Omron-M6-Comfort-Pressure-Monitors/...
https://www.amazon.co.uk/Salter-Automatic-Irregular-Heartbea...
I figure this will be true for Omron's watch too.