Many companies are introducing wrist-worn bands that track your activity levels, calculate calories burned, monitor your heart rate, etc. One drawback to the wrist-worn form factor is that it limits the skin surface area that can be used for sensing. Flexible electronics are being developed that can conform to body contours. As this type of technology advances, such tracking devices will need to be designed to access more skin area. It will be challenging to maintain breathability so the skin is not irritated.
Advances in adhesive technology will not be the answer. Anything mechanically secured to the skin will cause irritation over time. Even the slightest pressure on the skin, if constant over time, will cause irritation. Systems that embed sensors in clothing have potential. The problem of maintaining signal integrity will need to be solved for such systems, though, as even slight movement can cause problems.
Touch-free monitors could provide another solution. E.g., video that captures blood flow in the face. I can envision that touch free sensors won’t be worn by individuals but will be present in the environment around us: walk through a doorway and get a read-out of your heart rate and blood pressure. Ubiquitous, continuous monitoring will take the place of discrete devices.