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One afternoon in mid-October, I lugged two boxes, weighing a total of 65 pounds, up three flights of stairs. This was the first sign that my new full-body scanner was anything but an ordinary scale. I unboxed the hardware—a mirror and a flat plastic disc about the size of a turntable—and then downloaded an iPhone app, which instructed me to undress. And so there I was, in a pair of tight-fitting boxer briefs, waiting for a firmware update from Naked Labs.

On a regular bathroom scale, my five-foot-ten frame tips in at a little over 200 pounds. Calculate my body-mass index, and I’m a 29.8—which is considered overweight, almost obese. But the BMI is a bit of statistical snake oil. The formula was designed in the 1800s by a mathematician, not a doctor, and its intended purpose was to study whole populations rather than an individual person.

Naked Labs promises an entirely different way of measuring. Its $1,395 scanner, powered by Intel RealSense depth sensors, is billed as the first in-home product that can track not only fat and lean mass but also body circumferences and progress over time. The company’s proprietary algorithms, which are based on the U.S. Navy’s body-composition formula, make estimates based on age, weight, and height, as well as optical head-to-toe measurements, like a high-tech tailor measuring your body’s surface shape. Part of the device’s eye-popping price is what amounts to a lifetime membership to Naked Labs’ analytics and cloud computing. With no monthly fee, it’s an outlier in the flood of subscription-based fitness technologies. I was eager to see how the device stacked up. Or really, how I did.

For the past year, I’ve done CrossFit twice a week. But in a bid to transform some of my abdominal paunch into muscle, I resolved to hit the gym six days a week for six weeks. To track my progress, I stripped down on Sundays for a weekly Naked Labs scan.

For the first test, I paired the mirror and scale (the plastic disc) over Bluetooth. Then the app instructed me to put down my phone and step on. I gave it a whirl—the plate spins you clockwise. Eventually a gray avatar popped up on my phone’s screen. I looked like the Silver Surfer gone soft around the middle. The algorithms put my body fat at 20.3 percent. That was a slight ego boost, since it’s within the “acceptable” range (18 to 24 percent, according to the American Council on Exercise). With a scanner, though, my hope was that I’d start seeing where I was shedding fat and where I was making gains.

Of course, this isn’t Silicon Valley’s first shot at self-quantification for fitness obsessives, and these devices come with serious trade-offs. Tech companies harvest far more data than they reveal to their users. They play croupier, and you’re taking a spin at roulette—in my case, by uploading revealing images of myself. Two weeks into my trial, I began having second thoughts about my upcoming scan. Naked Labs anonymizes its data for various purposes (whatever that means) but explicitly warns that it will turn over any user information to law enforcement if necessary. I found no option for blurring out certain body parts, so I pulled a neoprene wetsuit hood over my face before my next go.

After six weeks of an intensive core and rowing circuit, the scanner showed that I reduced four pounds of fat mass and transformed two pounds into lean mass. And the scans proved revealing in other ways: my body is asymmetrical, and I was surprised to discover that my left leg was slightly larger than my right one. By the final scan, my body fat shrank from 20.3 to 18.6 percent, plus or minus the 2.5 percent margin of error.

, a researcher at the University of Hawaii who uses optical scanners to study fat deposition and cancer risk, confirmed my suspicions: my scans showed something that weight-based formulas cannot, and what the BMI treats as excess weight could mostly be attributed to my non-fat mass. Shepherd, who has partnered with Naked Labs, said the data is particularly useful in showing where fat is deposited. For athletes, scan data can also improve estimates of resting metabolic rate, evaluate the effectiveness of training, and compare muscle symmetry. For me, the scans motivated me to do more pistol squats on my right leg.

In the end, I saw more measurable results than I expected. I lost 2.2 pounds. On an ordinary scale, that’s practically meaningless. But combined with the estimated gains in lean mass, and the inch or so I trimmed off my waist and stomach, it felt more significant. If I keep at it, I’ll get these exacting measurements for the foreseeable future, along with access to the company’s analytics and algorithms, which it vows to keep improving. As for the downsides, Naked’s scale and app are useless without Wi-Fi. The hefty mirror and scale combo takes up a lot of real estate in my apartment, and I wonder if it will soon be rendered obsolete as more smartphones come equipped with similar optical-recognition technology.

If looking at yourself in the mirror gets you down, this device probably isn’t for you. And as Shepherd put it, “If you just want weight loss, you can get a scale.” But 3-D scanners calculate fat loss in ways that calipers and tailor’s tape do not, and you can see the changes. “This will measure how much fat you’re losing and can tell you how much muscle you’ve gained, and where you lost and gained.” Which, he said, can prove motivating. At the very least, watching how my avatar shaped up against the Silver Surfer gave me an extra incentive to hit the gym.