Which measurement are these cuffless wearables trying to track?

Blood pressure is the measurement these cuffless wearables try to track. Rather than inflating a cuff around the arm to physically measure the force of blood against artery walls, these devices use optical sensors on the wrist to estimate blood pressure indirectly from things like the timing and shape of the pulse, avoiding the bulky and briefly uncomfortable process of a traditional cuff reading.

Eye color and shoe size are simple physical traits with no connection to cardiovascular monitoring, and no wearable device measures either of them, so they serve here only as clearly implausible alternatives.

Despite the convenience of cuffless devices, their accuracy still generally trails that of traditional cuff-based blood pressure monitors, which is why researchers continue working to validate and calibrate them before they can be trusted for serious everyday medical decisions.