Sensors & Trackers
Sensors and trackers are where measurement begins: the components that convert a physical quantity into a signal a system can work with. Optical sensors read pulse from light, inertial sensors read motion, satellite receivers read position, and biosensors read physiology. Each has a characteristic strength and a characteristic failure mode, and the fidelity of this stage caps everything downstream, which is why the choice of sensor is the foundation of any measurement system.
Sensors & Trackers
Optical sensing
Reading light
Optical sensors infer a signal from how light interacts with tissue, most commonly estimating pulse from reflected light. They are comfortable and cheap, suited to continuous wear, but vulnerable to motion that disturbs the optical path. Their strength is convenience; their weakness is accuracy under vigorous movement.
Inertial sensing
Reading motion
Inertial sensors measure acceleration and rotation, and fused together they yield orientation and derived motion metrics. They are ubiquitous and inexpensive, and almost every cadence, stride, or repetition figure rests on them. Their accuracy depends on the fusion that combines their complementary, individually unreliable signals.
Position sensing
Reading place
Satellite receivers compute position from navigation signals, accurate to a handful of meters over open ground but degraded among buildings and dense cover. For tight, crowded, or indoor settings, venue based positioning takes over. The right position sensor depends entirely on the scale and environment of the activity.
Physiological sensing
Reading the body
Biosensors read signals from the body itself, from heart activity to metabolic markers, sometimes through the skin and sometimes through contact electrodes. These extend sensing past movement into physiology, and they tend to carry the most sensitive data, which makes how that data is handled a central rather than incidental concern.