The $249 Gem UV Necklace Found What Shade Couldn't Hide

By Priya Raman

A $249 necklace caught what a patio umbrella, a fan, and a reviewer's own assumptions all missed: UV exposure kept climbing while she sat in the shade. Half an hour into an outdoor party in Los Angeles during a 90-degree August heat wave, The Verge's Sheena Vasani felt exhausted, dizzy, and nauseous — symptoms consistent with heat exhaustion. The companion app for Gem, a UV-tracking pendant from a company called The90, warned at roughly the same time that her UV exposure had risen considerably.

The umbrella didn't repel UV radiation. It rarely can, because radiation reflects and scatters off objects in the environment. Full protection under shade is close to impossible. Heat and UV are separate problems, and the reviewer had mistakenly assumed the fan plus shade covered both.

What did the device actually change?

The episode prompted a discovery the sensor never diagnosed: one of her medications increases heat sensitivity, which explained similar episodes stretching back years. The Gem didn't detect anything medical. It simply pushed her to investigate what she might otherwise have dismissed.

The pendant measures UVA and UVB separately rather than pulling a regional UV forecast. That distinction matters. UVB drives sunburn and vitamin D production; UVA contributes to premature aging even without visible burning. The reviewer — Indian, rarely sunburned thanks to higher melanin content, living walking distance from an LA beach — had assumed her exposure was manageable. It wasn't, at least not in the way she expected.

How does the hardware hold up?

The circular pendant ships with a thin titanium chain in gold or silver tones, wearable enough that Vasani said she'd wear it even without tracking. Battery life ran almost exactly the advertised week, and an included charging dock handles recharging. The90 plans a hat clip and bag tag for early next year, aimed at people who'd rather not wear a necklace.

The mobile app carries most of the experience. It offers:

• Easy-to-read graphs and jargon-light explanations
• An optional skin profile built from skin type, sensitivities, clothing, and sunscreen use
• Estimated vitamin D production and circadian light benefits
• Estimated nitric-oxide-related benefits
• Cumulative and recent accumulated UVA exposure, plus weekly trends
• A Skin Aging Zone with personalized skincare advice
• A sunburn countdown, sunscreen reminders, and a daily Sun Score

Note what those numbers are: predictions, not direct measurements of how a body responds to sunlight. The company encourages a daily Sun Score of 90, balancing sunlight's benefits against overexposure risk. Vasani found the context useful but said the individual estimates proved more revealing than the composite score.

Where does the tracking fall short?

The readings responded quickly when moving between sun, shade, and indoors — even near windows. But she couldn't independently verify sensor accuracy. Worse, the Gem sometimes failed to register outdoor time entirely. The cause: on iPhone, the app must keep running in the background, because the sensor stores no measurements itself. Close the app, lose the data. Android behavior went untested.

The vitamin D countdown wobbled badly. In one test, its estimate of needed additional sunlight dropped from several hours to under an hour, then climbed past six hours minutes later. The sunburn timer fluctuated similarly. Vasani stopped trusting the exact figures and read the broader picture instead: too much sun or too little.

What surprised the tester most?

Two findings cut against expectation. First, her weekly UVB accumulation ran low despite the sunny location — she fell short of the app's estimated sunlight-derived vitamin D target almost daily, which sent her researching how melanin, while protective, slows vitamin D production from sun. Second, her exposure sat at extremes: either too little to hit targets or enough to raise overexposure concerns, even in perceived shade.

Is it worth $249?

At $249 — $149 at the time of publication — the Gem carries no subscription, which softens the cost slightly. Vasani can't justify it for her indoor-heavy life. She sees the appeal for people who spend considerable time outside or want deliberate sun protection. Her closing wishes: clearer app guidance and tracking that survives a closed app.

The bigger shift, she writes, was mental — thinking less about how her body looks in the sun and more about how she's treating it. For buyers weighing the price, the unresolved questions about countdown stability and background-app dependency are worth watching before The90's clip and tag accessories arrive next year.