Wait, Amazon's New Wearable Needs to See Me in My Underwear? Amazon says your semi-nude pictures will be automatically deleted from its servers after 3D body images are rendered. In return, you'll get an accurate estimate of your body fat percentage.

To get the most out of Amazon's new wearable wristband, you'll need to send the company semi-nude pictures of yourself.

The Halo is a fitness tracker that promises to improve your health. But to fully enjoy the benefits, Amazon needs some personal data, including how much fat is on your body. The company could've just asked for your weight and height. However, the health experts behind Halo want to instead calculate your body fat percentage, citing it as a better indicator for health and longevity.

To get an accurate measurement, the company created "Body," a feature in the app for Halo that uses computer vision and machine-learning algorithms to estimate your body fat percentage. The catch? The technology only works if it can actually view images of your semi-nude self.

In a blog post, Amazon Medical Officer Maulik Majmudar wrote how users can do this with the help of the Halo app and their smartphone's camera: "You'll need to wear tight, minimal clothing (think a sports bra and bike shorts for women; boxers or briefs for men), tie up your hair, and keep about 4-6 feet of space between you and your phone. Uniform lighting from the front is ideal. When you're ready, the Amazon Halo app shows you exactly how to stand and guides you through taking four scan images—front, back, and each side."

The pictures are then sent to Amazon's servers, which can begin rendering a 3D model of your body and calculating the body fat percentage estimate. To keep the model accurate, you should also continue sending Amazon your semi nudes. "We recommend taking scans every 2 weeks and observe trends over a longer duration to track progress," Majmudar added.

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If this all sounds like a terrible idea, Amazon says don't worry. "Your body scan images are automatically deleted from the cloud after processing," Majmudar wrote. "After that, the images and resulting personalized 3D body model are only stored locally on your phone. This means no one but you ever sees them unless you choose to share them with a friend or coach—or for a future #transformationtuesday post."

Your data on the Halo app can also be deleted. But conversely, if you trust Amazon, you can save all your body-scanned images to your Amazon cloud storage account. "You can opt back out any time directly from the Amazon Halo app and your images will automatically be deleted from the cloud," Majmudar added.

Amazon says it built Halo with privacy in mind. Still, the fitness tracker is asking for users to give up private data that goes well beyond heartbeats and calories tracked. The other eyebrow-raising feature, called Tone, says it can measure your stress levels by hearing your voice. However, to get the most out of it, Amazon recommends you let the feature run on your Halo smartband throughout the day. This will allow the fitness tracker's microphones to take short samples of your speech to measure when you're stressed out, feeling sad, or happy.

The constant recording sounds pretty invasive. But again, Amazon says don't worry. In this case, the speech samples are never sent to the company's servers. "If you choose to turn the feature on by creating a personal voice profile, your Tone speech samples are processed locally on your phone and deleted automatically after processing," Majmudar wrote.

The company also claims Tone is smart enough to only recognize your voice, and not others. So the microphones on the fitness band will remain off if your friend or family member is talking to you.

Still, all this assumes Halo will run without any bugs or be abused when history has shown tech products can often infringe on people's privacy, intentionally or not.

Stay tuned for our review of Amazon's Halo, when we can go over the privacy implications. For now, the product is up for sale for $64.99, but only for users who request early access to the device. Once six months is up, buyers will also need to pay $3.99 a month for body fat scanning, voice analysis, and other functions.