Doctors warn that the Apple Watch's hypertension detection feature risks providing false reassurance and should not be used as a substitute for traditional blood pressure monitoring. A validation study that Apple submitted to the US Food and Drug Administration compared the feature to home monitoring for 30 days. Only 41.2% of people with undiagnosed hypertension received a warning, including participants without hypertension. 92.3% of people with hypertension did not receive a warning and 7.7% received an inappropriate warning. The researchers reported in JAMA that the results provide only moderate evidence to rule out hypertension and weak evidence to confirm it. The positive predictive value of function was 69.1% (95% confidence interval 76.6% to 81.3%).