Then, on Thursday, consumers were introduced to what could be the next health tracker trend: a wearable device that tracks a user’s sun exposure. Launched by tech startup The90 and helmed by CEO and co-founder Stacy Salvi, a former director at Google-owned Fitbit, the new device launched with a limited run but a wide runway, she told Glossy. “[The Gem wearable] has a photodiode sensor that detects UVA, which is the aging UV, and UVB, which is the burning UV,” Salvi told Glossy.