So check out this video. It's a bit heavy on the tech-ese (I got lost a few times during the explanations), but the bottom line is that our technology is to the point that a video camera can look at you and tell what your pulse rate is. No wires. No sensors. Just an iPad camera. Not even a great camera! How does it do this? "Magic" seems a good enough answer to me, but it appears that as our body pumps blood through our system, our skin color changes. It's an imperceptible change to our vision, but computers can tell the difference. At that point, it's easy--just count how many times the person is changing color per minute.
We live in a crazy world, my friends. I love technology. Now if I can just get a hoverboard and a robot maid, I'll be pretty much set . . .