Wearable fitness devices are influencing today’s medical devices that target clinical and everyday applications. Some of the innovation involves new modalities of measurement: for example an iPhone that analyzes your eyeball to determine blood pressure. But fundamentally the challenge has shifted from determining how to make accurate and precise measurements to how to enable a compact wearable device which supports adequate battery life and wireless data communication. There are also challenges in making measurements on conveniently worn devices. For example, it is very hard to measure ECG and breathing on a wrist worn device.