Aura at CES 2019 introduced an Apple Watch "Smart Strap" designed to measure weight, water, fat, and muscle via electrodes built into the band. The strap didn't end up launching in 2019, but Aura says that it's set to launch in March 2020, with pre-orders available now.
The Aura Strap, which is priced at $99, claims to allow users to measure their body composition and track their hydration levels and fitness progress. Aura says the band uses bioimpedance to analyze the upper body, tracking lung performance and changes in breathing, comparing that information with pulse data.
The band is able to assess the risk of heart failure and notify the user, though this is something that newer Apple Watch models can do on their own without the need for an additional strap. Measuring body composition and hydration is not something the Apple Watch can do on its own, though testing will need to be done to see how accurate the Aura strap is in practice.
The Aura Strap is available in four color options, including black, green, red, and gray, and it attaches to the Apple Watch using the standard Apple Watch lugs. According to Aura, the strap transfers results to the watch "via an ultrasound interface" and it works for up to six months on a single battery. It has the same waterproof specifications as the watch and is able to sync with HealthKit.
Aura is taking pre-orders for the watch as of today, with the device set to begin shipping out to customers starting in March 2020.