You need the sun for your body to create vitamin D.
A function of a smart watch that is set up for your skin type (so you don’t get sunburns) and measures the daily dosage of sun you get. During the day you can see how much sun time you still need (also based on your location, time of year, and time of day), and how many international units of vitamin you need to take that day if you don’t get any more sun exposure.
Many pools have a semi-transparent canopy stretched above part of it. The sun, however, is always moving, and vast areas of the pool are not under the shadow.
Automatically adjust the canopy’s position by sensing the position of the sun and recoiling and releasing – changing the lengths of the ropes keeping the canopy tight.
To help remind you when you need to apply more sunscreen.
Have a “smart” patch you stick on your exposed skin that monitors the amount of sun you are exposed to and alerts you to put some more sunscreen when you have reached a certain exposure level.