As soon as it's on my head, Google Glass picks up my pulse. Late for the meeting, I had scrambled up to the third floor of the MIT Media Lab for this demo, and my racing heart shows it. I huff and puff while Javier Hernandez, the project's leader, explains how it works. As he talks, my heart beat settles down before my eyes: 79 beats per minute, 73, 69.Hernandez has taught Glass to measure vital signs like pulse and respiration using just the headset's built-in gyroscope, accelerometer and camera. They pick up the subtle head motion caused by the beating of the heart, and tease out the rise and fall of a breath from other movements.