What is Stella & how does it work? Stella is a wearable that measures UV radiation levels, and then notifies you when you are about to be overexposed to UV rays. Stella also tracks your activity levels, sleeping patterns, and daily Vitamin D intake from the sun. All a user has to do is, select their skin type (Fitzpatrick Scale), a form of protection (SPF) and allow Stella to do the rest. Now you will know when exactly you should seek shade and re-apply sunscreen. Subscribe to Stella and we'll notify you when we begin to take pre-orders.