For the last several years Samsung has included a heart rate monitor inside the flash and camera system on the back of Galaxy phones. And, believe it or not, most people still don't know it exists.
Better yet, with the Galaxy S9 Samsung added a blood pressure monitor to the phones capabilities. Simply open the Samsung S-Health app on your phone, and enjoy everything is has to offer.
I use it to track my steps, watch my water and food intake, and I can even test my blood pressure and stress levels using the sensor on the back. It'll make your finger glow like E.T. but it takes accurate information that will help you be happier and healthier.