Review: UV-tracking Gem necklace prompts a rethink of sun exposure and health
A Verge writer tested the Gem, a necklace from The90 that measures UVA and UVB radiation. It helped her better understand sun exposure and health, though some of the app's estimates were less useful than others.
Sheena Vasani, a writer at the technology site The Verge, tested the Gem, a necklace from the company The90 that uses a sensor to measure UVA and UVB radiation separately and sends the data to a mobile app. The device costs $249, and was discounted to $149 when the review was published.
An unexpected warning
In August, at an outdoor family party in Los Angeles where temperatures reached the 90s Fahrenheit (around 32 °C), the author sat under a patio umbrella with a fan nearby. Half an hour later she felt exhausted, dizzy and nauseous, symptoms consistent with heat exhaustion. Around the same time, the app warned that her UV exposure had risen considerably. She concluded that an umbrella does not fully protect against UV, because radiation can be reflected or scattered by surrounding objects. She later learned that one of her medications increases sensitivity to heat.
What the app measures
The app estimates a range of metrics: vitamin D production, circadian light benefits, cumulative UVA exposure, time to sunburn and a daily Sun Score. The company suggests aiming for a score of 90. Users can create a skin profile to personalize the estimates, but these remain predictions rather than direct measurements of how the body responds to sunlight.
The author found that the vitamin D and sunburn countdowns fluctuated sharply, so she paid less attention to the exact times. She also found that the app must keep running in the background, since measurements are not stored on the sensor. Battery life lasted about a week. The90 plans to release a hat clip and a bag tag early next year.
Verdict
The author says the device showed her that her exposure often falls at one of two extremes: too little or enough to raise concern. At $249 she cannot justify the price, given how much time she spends indoors, but she notes there is no subscription.
